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0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * Budget Fair Queueing (BFQ) I/O scheduler.
0004  *
0005  * Based on ideas and code from CFQ:
0006  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
0007  *
0008  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
0009  *            Paolo Valente <paolo.valente@unimore.it>
0010  *
0011  * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
0012  *                    Arianna Avanzini <avanzini@google.com>
0013  *
0014  * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
0015  *
0016  * BFQ is a proportional-share I/O scheduler, with some extra
0017  * low-latency capabilities. BFQ also supports full hierarchical
0018  * scheduling through cgroups. Next paragraphs provide an introduction
0019  * on BFQ inner workings. Details on BFQ benefits, usage and
0020  * limitations can be found in Documentation/block/bfq-iosched.rst.
0021  *
0022  * BFQ is a proportional-share storage-I/O scheduling algorithm based
0023  * on the slice-by-slice service scheme of CFQ. But BFQ assigns
0024  * budgets, measured in number of sectors, to processes instead of
0025  * time slices. The device is not granted to the in-service process
0026  * for a given time slice, but until it has exhausted its assigned
0027  * budget. This change from the time to the service domain enables BFQ
0028  * to distribute the device throughput among processes as desired,
0029  * without any distortion due to throughput fluctuations, or to device
0030  * internal queueing. BFQ uses an ad hoc internal scheduler, called
0031  * B-WF2Q+, to schedule processes according to their budgets. More
0032  * precisely, BFQ schedules queues associated with processes. Each
0033  * process/queue is assigned a user-configurable weight, and B-WF2Q+
0034  * guarantees that each queue receives a fraction of the throughput
0035  * proportional to its weight. Thanks to the accurate policy of
0036  * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
0037  * processes issuing sequential requests (to boost the throughput),
0038  * and yet guarantee a low latency to interactive and soft real-time
0039  * applications.
0040  *
0041  * In particular, to provide these low-latency guarantees, BFQ
0042  * explicitly privileges the I/O of two classes of time-sensitive
0043  * applications: interactive and soft real-time. In more detail, BFQ
0044  * behaves this way if the low_latency parameter is set (default
0045  * configuration). This feature enables BFQ to provide applications in
0046  * these classes with a very low latency.
0047  *
0048  * To implement this feature, BFQ constantly tries to detect whether
0049  * the I/O requests in a bfq_queue come from an interactive or a soft
0050  * real-time application. For brevity, in these cases, the queue is
0051  * said to be interactive or soft real-time. In both cases, BFQ
0052  * privileges the service of the queue, over that of non-interactive
0053  * and non-soft-real-time queues. This privileging is performed,
0054  * mainly, by raising the weight of the queue. So, for brevity, we
0055  * call just weight-raising periods the time periods during which a
0056  * queue is privileged, because deemed interactive or soft real-time.
0057  *
0058  * The detection of soft real-time queues/applications is described in
0059  * detail in the comments on the function
0060  * bfq_bfqq_softrt_next_start. On the other hand, the detection of an
0061  * interactive queue works as follows: a queue is deemed interactive
0062  * if it is constantly non empty only for a limited time interval,
0063  * after which it does become empty. The queue may be deemed
0064  * interactive again (for a limited time), if it restarts being
0065  * constantly non empty, provided that this happens only after the
0066  * queue has remained empty for a given minimum idle time.
0067  *
0068  * By default, BFQ computes automatically the above maximum time
0069  * interval, i.e., the time interval after which a constantly
0070  * non-empty queue stops being deemed interactive. Since a queue is
0071  * weight-raised while it is deemed interactive, this maximum time
0072  * interval happens to coincide with the (maximum) duration of the
0073  * weight-raising for interactive queues.
0074  *
0075  * Finally, BFQ also features additional heuristics for
0076  * preserving both a low latency and a high throughput on NCQ-capable,
0077  * rotational or flash-based devices, and to get the job done quickly
0078  * for applications consisting in many I/O-bound processes.
0079  *
0080  * NOTE: if the main or only goal, with a given device, is to achieve
0081  * the maximum-possible throughput at all times, then do switch off
0082  * all low-latency heuristics for that device, by setting low_latency
0083  * to 0.
0084  *
0085  * BFQ is described in [1], where also a reference to the initial,
0086  * more theoretical paper on BFQ can be found. The interested reader
0087  * can find in the latter paper full details on the main algorithm, as
0088  * well as formulas of the guarantees and formal proofs of all the
0089  * properties.  With respect to the version of BFQ presented in these
0090  * papers, this implementation adds a few more heuristics, such as the
0091  * ones that guarantee a low latency to interactive and soft real-time
0092  * applications, and a hierarchical extension based on H-WF2Q+.
0093  *
0094  * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
0095  * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
0096  * with O(log N) complexity derives from the one introduced with EEVDF
0097  * in [3].
0098  *
0099  * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
0100  *     Scheduler", Proceedings of the First Workshop on Mobile System
0101  *     Technologies (MST-2015), May 2015.
0102  *     http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
0103  *
0104  * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
0105  *     Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
0106  *     Oct 1997.
0107  *
0108  * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
0109  *
0110  * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
0111  *     First: A Flexible and Accurate Mechanism for Proportional Share
0112  *     Resource Allocation", technical report.
0113  *
0114  * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
0115  */
0116 #include <linux/module.h>
0117 #include <linux/slab.h>
0118 #include <linux/blkdev.h>
0119 #include <linux/cgroup.h>
0120 #include <linux/ktime.h>
0121 #include <linux/rbtree.h>
0122 #include <linux/ioprio.h>
0123 #include <linux/sbitmap.h>
0124 #include <linux/delay.h>
0125 #include <linux/backing-dev.h>
0126 
0127 #include <trace/events/block.h>
0128 
0129 #include "elevator.h"
0130 #include "blk.h"
0131 #include "blk-mq.h"
0132 #include "blk-mq-tag.h"
0133 #include "blk-mq-sched.h"
0134 #include "bfq-iosched.h"
0135 #include "blk-wbt.h"
0136 
0137 #define BFQ_BFQQ_FNS(name)                      \
0138 void bfq_mark_bfqq_##name(struct bfq_queue *bfqq)           \
0139 {                                   \
0140     __set_bit(BFQQF_##name, &(bfqq)->flags);            \
0141 }                                   \
0142 void bfq_clear_bfqq_##name(struct bfq_queue *bfqq)          \
0143 {                                   \
0144     __clear_bit(BFQQF_##name, &(bfqq)->flags);      \
0145 }                                   \
0146 int bfq_bfqq_##name(const struct bfq_queue *bfqq)           \
0147 {                                   \
0148     return test_bit(BFQQF_##name, &(bfqq)->flags);      \
0149 }
0150 
0151 BFQ_BFQQ_FNS(just_created);
0152 BFQ_BFQQ_FNS(busy);
0153 BFQ_BFQQ_FNS(wait_request);
0154 BFQ_BFQQ_FNS(non_blocking_wait_rq);
0155 BFQ_BFQQ_FNS(fifo_expire);
0156 BFQ_BFQQ_FNS(has_short_ttime);
0157 BFQ_BFQQ_FNS(sync);
0158 BFQ_BFQQ_FNS(IO_bound);
0159 BFQ_BFQQ_FNS(in_large_burst);
0160 BFQ_BFQQ_FNS(coop);
0161 BFQ_BFQQ_FNS(split_coop);
0162 BFQ_BFQQ_FNS(softrt_update);
0163 #undef BFQ_BFQQ_FNS                     \
0164 
0165 /* Expiration time of async (0) and sync (1) requests, in ns. */
0166 static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
0167 
0168 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
0169 static const int bfq_back_max = 16 * 1024;
0170 
0171 /* Penalty of a backwards seek, in number of sectors. */
0172 static const int bfq_back_penalty = 2;
0173 
0174 /* Idling period duration, in ns. */
0175 static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
0176 
0177 /* Minimum number of assigned budgets for which stats are safe to compute. */
0178 static const int bfq_stats_min_budgets = 194;
0179 
0180 /* Default maximum budget values, in sectors and number of requests. */
0181 static const int bfq_default_max_budget = 16 * 1024;
0182 
0183 /*
0184  * When a sync request is dispatched, the queue that contains that
0185  * request, and all the ancestor entities of that queue, are charged
0186  * with the number of sectors of the request. In contrast, if the
0187  * request is async, then the queue and its ancestor entities are
0188  * charged with the number of sectors of the request, multiplied by
0189  * the factor below. This throttles the bandwidth for async I/O,
0190  * w.r.t. to sync I/O, and it is done to counter the tendency of async
0191  * writes to steal I/O throughput to reads.
0192  *
0193  * The current value of this parameter is the result of a tuning with
0194  * several hardware and software configurations. We tried to find the
0195  * lowest value for which writes do not cause noticeable problems to
0196  * reads. In fact, the lower this parameter, the stabler I/O control,
0197  * in the following respect.  The lower this parameter is, the less
0198  * the bandwidth enjoyed by a group decreases
0199  * - when the group does writes, w.r.t. to when it does reads;
0200  * - when other groups do reads, w.r.t. to when they do writes.
0201  */
0202 static const int bfq_async_charge_factor = 3;
0203 
0204 /* Default timeout values, in jiffies, approximating CFQ defaults. */
0205 const int bfq_timeout = HZ / 8;
0206 
0207 /*
0208  * Time limit for merging (see comments in bfq_setup_cooperator). Set
0209  * to the slowest value that, in our tests, proved to be effective in
0210  * removing false positives, while not causing true positives to miss
0211  * queue merging.
0212  *
0213  * As can be deduced from the low time limit below, queue merging, if
0214  * successful, happens at the very beginning of the I/O of the involved
0215  * cooperating processes, as a consequence of the arrival of the very
0216  * first requests from each cooperator.  After that, there is very
0217  * little chance to find cooperators.
0218  */
0219 static const unsigned long bfq_merge_time_limit = HZ/10;
0220 
0221 static struct kmem_cache *bfq_pool;
0222 
0223 /* Below this threshold (in ns), we consider thinktime immediate. */
0224 #define BFQ_MIN_TT      (2 * NSEC_PER_MSEC)
0225 
0226 /* hw_tag detection: parallel requests threshold and min samples needed. */
0227 #define BFQ_HW_QUEUE_THRESHOLD  3
0228 #define BFQ_HW_QUEUE_SAMPLES    32
0229 
0230 #define BFQQ_SEEK_THR       (sector_t)(8 * 100)
0231 #define BFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
0232 #define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
0233     (get_sdist(last_pos, rq) >          \
0234      BFQQ_SEEK_THR &&               \
0235      (!blk_queue_nonrot(bfqd->queue) ||     \
0236       blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
0237 #define BFQQ_CLOSE_THR      (sector_t)(8 * 1024)
0238 #define BFQQ_SEEKY(bfqq)    (hweight32(bfqq->seek_history) > 19)
0239 /*
0240  * Sync random I/O is likely to be confused with soft real-time I/O,
0241  * because it is characterized by limited throughput and apparently
0242  * isochronous arrival pattern. To avoid false positives, queues
0243  * containing only random (seeky) I/O are prevented from being tagged
0244  * as soft real-time.
0245  */
0246 #define BFQQ_TOTALLY_SEEKY(bfqq)    (bfqq->seek_history == -1)
0247 
0248 /* Min number of samples required to perform peak-rate update */
0249 #define BFQ_RATE_MIN_SAMPLES    32
0250 /* Min observation time interval required to perform a peak-rate update (ns) */
0251 #define BFQ_RATE_MIN_INTERVAL   (300*NSEC_PER_MSEC)
0252 /* Target observation time interval for a peak-rate update (ns) */
0253 #define BFQ_RATE_REF_INTERVAL   NSEC_PER_SEC
0254 
0255 /*
0256  * Shift used for peak-rate fixed precision calculations.
0257  * With
0258  * - the current shift: 16 positions
0259  * - the current type used to store rate: u32
0260  * - the current unit of measure for rate: [sectors/usec], or, more precisely,
0261  *   [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
0262  * the range of rates that can be stored is
0263  * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
0264  * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
0265  * [15, 65G] sectors/sec
0266  * Which, assuming a sector size of 512B, corresponds to a range of
0267  * [7.5K, 33T] B/sec
0268  */
0269 #define BFQ_RATE_SHIFT      16
0270 
0271 /*
0272  * When configured for computing the duration of the weight-raising
0273  * for interactive queues automatically (see the comments at the
0274  * beginning of this file), BFQ does it using the following formula:
0275  * duration = (ref_rate / r) * ref_wr_duration,
0276  * where r is the peak rate of the device, and ref_rate and
0277  * ref_wr_duration are two reference parameters.  In particular,
0278  * ref_rate is the peak rate of the reference storage device (see
0279  * below), and ref_wr_duration is about the maximum time needed, with
0280  * BFQ and while reading two files in parallel, to load typical large
0281  * applications on the reference device (see the comments on
0282  * max_service_from_wr below, for more details on how ref_wr_duration
0283  * is obtained).  In practice, the slower/faster the device at hand
0284  * is, the more/less it takes to load applications with respect to the
0285  * reference device.  Accordingly, the longer/shorter BFQ grants
0286  * weight raising to interactive applications.
0287  *
0288  * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
0289  * depending on whether the device is rotational or non-rotational.
0290  *
0291  * In the following definitions, ref_rate[0] and ref_wr_duration[0]
0292  * are the reference values for a rotational device, whereas
0293  * ref_rate[1] and ref_wr_duration[1] are the reference values for a
0294  * non-rotational device. The reference rates are not the actual peak
0295  * rates of the devices used as a reference, but slightly lower
0296  * values. The reason for using slightly lower values is that the
0297  * peak-rate estimator tends to yield slightly lower values than the
0298  * actual peak rate (it can yield the actual peak rate only if there
0299  * is only one process doing I/O, and the process does sequential
0300  * I/O).
0301  *
0302  * The reference peak rates are measured in sectors/usec, left-shifted
0303  * by BFQ_RATE_SHIFT.
0304  */
0305 static int ref_rate[2] = {14000, 33000};
0306 /*
0307  * To improve readability, a conversion function is used to initialize
0308  * the following array, which entails that the array can be
0309  * initialized only in a function.
0310  */
0311 static int ref_wr_duration[2];
0312 
0313 /*
0314  * BFQ uses the above-detailed, time-based weight-raising mechanism to
0315  * privilege interactive tasks. This mechanism is vulnerable to the
0316  * following false positives: I/O-bound applications that will go on
0317  * doing I/O for much longer than the duration of weight
0318  * raising. These applications have basically no benefit from being
0319  * weight-raised at the beginning of their I/O. On the opposite end,
0320  * while being weight-raised, these applications
0321  * a) unjustly steal throughput to applications that may actually need
0322  * low latency;
0323  * b) make BFQ uselessly perform device idling; device idling results
0324  * in loss of device throughput with most flash-based storage, and may
0325  * increase latencies when used purposelessly.
0326  *
0327  * BFQ tries to reduce these problems, by adopting the following
0328  * countermeasure. To introduce this countermeasure, we need first to
0329  * finish explaining how the duration of weight-raising for
0330  * interactive tasks is computed.
0331  *
0332  * For a bfq_queue deemed as interactive, the duration of weight
0333  * raising is dynamically adjusted, as a function of the estimated
0334  * peak rate of the device, so as to be equal to the time needed to
0335  * execute the 'largest' interactive task we benchmarked so far. By
0336  * largest task, we mean the task for which each involved process has
0337  * to do more I/O than for any of the other tasks we benchmarked. This
0338  * reference interactive task is the start-up of LibreOffice Writer,
0339  * and in this task each process/bfq_queue needs to have at most ~110K
0340  * sectors transferred.
0341  *
0342  * This last piece of information enables BFQ to reduce the actual
0343  * duration of weight-raising for at least one class of I/O-bound
0344  * applications: those doing sequential or quasi-sequential I/O. An
0345  * example is file copy. In fact, once started, the main I/O-bound
0346  * processes of these applications usually consume the above 110K
0347  * sectors in much less time than the processes of an application that
0348  * is starting, because these I/O-bound processes will greedily devote
0349  * almost all their CPU cycles only to their target,
0350  * throughput-friendly I/O operations. This is even more true if BFQ
0351  * happens to be underestimating the device peak rate, and thus
0352  * overestimating the duration of weight raising. But, according to
0353  * our measurements, once transferred 110K sectors, these processes
0354  * have no right to be weight-raised any longer.
0355  *
0356  * Basing on the last consideration, BFQ ends weight-raising for a
0357  * bfq_queue if the latter happens to have received an amount of
0358  * service at least equal to the following constant. The constant is
0359  * set to slightly more than 110K, to have a minimum safety margin.
0360  *
0361  * This early ending of weight-raising reduces the amount of time
0362  * during which interactive false positives cause the two problems
0363  * described at the beginning of these comments.
0364  */
0365 static const unsigned long max_service_from_wr = 120000;
0366 
0367 /*
0368  * Maximum time between the creation of two queues, for stable merge
0369  * to be activated (in ms)
0370  */
0371 static const unsigned long bfq_activation_stable_merging = 600;
0372 /*
0373  * Minimum time to be waited before evaluating delayed stable merge (in ms)
0374  */
0375 static const unsigned long bfq_late_stable_merging = 600;
0376 
0377 #define RQ_BIC(rq)      ((struct bfq_io_cq *)((rq)->elv.priv[0]))
0378 #define RQ_BFQQ(rq)     ((rq)->elv.priv[1])
0379 
0380 struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
0381 {
0382     return bic->bfqq[is_sync];
0383 }
0384 
0385 static void bfq_put_stable_ref(struct bfq_queue *bfqq);
0386 
0387 void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
0388 {
0389     /*
0390      * If bfqq != NULL, then a non-stable queue merge between
0391      * bic->bfqq and bfqq is happening here. This causes troubles
0392      * in the following case: bic->bfqq has also been scheduled
0393      * for a possible stable merge with bic->stable_merge_bfqq,
0394      * and bic->stable_merge_bfqq == bfqq happens to
0395      * hold. Troubles occur because bfqq may then undergo a split,
0396      * thereby becoming eligible for a stable merge. Yet, if
0397      * bic->stable_merge_bfqq points exactly to bfqq, then bfqq
0398      * would be stably merged with itself. To avoid this anomaly,
0399      * we cancel the stable merge if
0400      * bic->stable_merge_bfqq == bfqq.
0401      */
0402     bic->bfqq[is_sync] = bfqq;
0403 
0404     if (bfqq && bic->stable_merge_bfqq == bfqq) {
0405         /*
0406          * Actually, these same instructions are executed also
0407          * in bfq_setup_cooperator, in case of abort or actual
0408          * execution of a stable merge. We could avoid
0409          * repeating these instructions there too, but if we
0410          * did so, we would nest even more complexity in this
0411          * function.
0412          */
0413         bfq_put_stable_ref(bic->stable_merge_bfqq);
0414 
0415         bic->stable_merge_bfqq = NULL;
0416     }
0417 }
0418 
0419 struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
0420 {
0421     return bic->icq.q->elevator->elevator_data;
0422 }
0423 
0424 /**
0425  * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
0426  * @icq: the iocontext queue.
0427  */
0428 static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
0429 {
0430     /* bic->icq is the first member, %NULL will convert to %NULL */
0431     return container_of(icq, struct bfq_io_cq, icq);
0432 }
0433 
0434 /**
0435  * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
0436  * @q: the request queue.
0437  */
0438 static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q)
0439 {
0440     struct bfq_io_cq *icq;
0441     unsigned long flags;
0442 
0443     if (!current->io_context)
0444         return NULL;
0445 
0446     spin_lock_irqsave(&q->queue_lock, flags);
0447     icq = icq_to_bic(ioc_lookup_icq(q));
0448     spin_unlock_irqrestore(&q->queue_lock, flags);
0449 
0450     return icq;
0451 }
0452 
0453 /*
0454  * Scheduler run of queue, if there are requests pending and no one in the
0455  * driver that will restart queueing.
0456  */
0457 void bfq_schedule_dispatch(struct bfq_data *bfqd)
0458 {
0459     lockdep_assert_held(&bfqd->lock);
0460 
0461     if (bfqd->queued != 0) {
0462         bfq_log(bfqd, "schedule dispatch");
0463         blk_mq_run_hw_queues(bfqd->queue, true);
0464     }
0465 }
0466 
0467 #define bfq_class_idle(bfqq)    ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
0468 
0469 #define bfq_sample_valid(samples)   ((samples) > 80)
0470 
0471 /*
0472  * Lifted from AS - choose which of rq1 and rq2 that is best served now.
0473  * We choose the request that is closer to the head right now.  Distance
0474  * behind the head is penalized and only allowed to a certain extent.
0475  */
0476 static struct request *bfq_choose_req(struct bfq_data *bfqd,
0477                       struct request *rq1,
0478                       struct request *rq2,
0479                       sector_t last)
0480 {
0481     sector_t s1, s2, d1 = 0, d2 = 0;
0482     unsigned long back_max;
0483 #define BFQ_RQ1_WRAP    0x01 /* request 1 wraps */
0484 #define BFQ_RQ2_WRAP    0x02 /* request 2 wraps */
0485     unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
0486 
0487     if (!rq1 || rq1 == rq2)
0488         return rq2;
0489     if (!rq2)
0490         return rq1;
0491 
0492     if (rq_is_sync(rq1) && !rq_is_sync(rq2))
0493         return rq1;
0494     else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
0495         return rq2;
0496     if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
0497         return rq1;
0498     else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
0499         return rq2;
0500 
0501     s1 = blk_rq_pos(rq1);
0502     s2 = blk_rq_pos(rq2);
0503 
0504     /*
0505      * By definition, 1KiB is 2 sectors.
0506      */
0507     back_max = bfqd->bfq_back_max * 2;
0508 
0509     /*
0510      * Strict one way elevator _except_ in the case where we allow
0511      * short backward seeks which are biased as twice the cost of a
0512      * similar forward seek.
0513      */
0514     if (s1 >= last)
0515         d1 = s1 - last;
0516     else if (s1 + back_max >= last)
0517         d1 = (last - s1) * bfqd->bfq_back_penalty;
0518     else
0519         wrap |= BFQ_RQ1_WRAP;
0520 
0521     if (s2 >= last)
0522         d2 = s2 - last;
0523     else if (s2 + back_max >= last)
0524         d2 = (last - s2) * bfqd->bfq_back_penalty;
0525     else
0526         wrap |= BFQ_RQ2_WRAP;
0527 
0528     /* Found required data */
0529 
0530     /*
0531      * By doing switch() on the bit mask "wrap" we avoid having to
0532      * check two variables for all permutations: --> faster!
0533      */
0534     switch (wrap) {
0535     case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
0536         if (d1 < d2)
0537             return rq1;
0538         else if (d2 < d1)
0539             return rq2;
0540 
0541         if (s1 >= s2)
0542             return rq1;
0543         else
0544             return rq2;
0545 
0546     case BFQ_RQ2_WRAP:
0547         return rq1;
0548     case BFQ_RQ1_WRAP:
0549         return rq2;
0550     case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
0551     default:
0552         /*
0553          * Since both rqs are wrapped,
0554          * start with the one that's further behind head
0555          * (--> only *one* back seek required),
0556          * since back seek takes more time than forward.
0557          */
0558         if (s1 <= s2)
0559             return rq1;
0560         else
0561             return rq2;
0562     }
0563 }
0564 
0565 #define BFQ_LIMIT_INLINE_DEPTH 16
0566 
0567 #ifdef CONFIG_BFQ_GROUP_IOSCHED
0568 static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
0569 {
0570     struct bfq_data *bfqd = bfqq->bfqd;
0571     struct bfq_entity *entity = &bfqq->entity;
0572     struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
0573     struct bfq_entity **entities = inline_entities;
0574     int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
0575     int class_idx = bfqq->ioprio_class - 1;
0576     struct bfq_sched_data *sched_data;
0577     unsigned long wsum;
0578     bool ret = false;
0579 
0580     if (!entity->on_st_or_in_serv)
0581         return false;
0582 
0583 retry:
0584     spin_lock_irq(&bfqd->lock);
0585     /* +1 for bfqq entity, root cgroup not included */
0586     depth = bfqg_to_blkg(bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
0587     if (depth > alloc_depth) {
0588         spin_unlock_irq(&bfqd->lock);
0589         if (entities != inline_entities)
0590             kfree(entities);
0591         entities = kmalloc_array(depth, sizeof(*entities), GFP_NOIO);
0592         if (!entities)
0593             return false;
0594         alloc_depth = depth;
0595         goto retry;
0596     }
0597 
0598     sched_data = entity->sched_data;
0599     /* Gather our ancestors as we need to traverse them in reverse order */
0600     level = 0;
0601     for_each_entity(entity) {
0602         /*
0603          * If at some level entity is not even active, allow request
0604          * queueing so that BFQ knows there's work to do and activate
0605          * entities.
0606          */
0607         if (!entity->on_st_or_in_serv)
0608             goto out;
0609         /* Uh, more parents than cgroup subsystem thinks? */
0610         if (WARN_ON_ONCE(level >= depth))
0611             break;
0612         entities[level++] = entity;
0613     }
0614     WARN_ON_ONCE(level != depth);
0615     for (level--; level >= 0; level--) {
0616         entity = entities[level];
0617         if (level > 0) {
0618             wsum = bfq_entity_service_tree(entity)->wsum;
0619         } else {
0620             int i;
0621             /*
0622              * For bfqq itself we take into account service trees
0623              * of all higher priority classes and multiply their
0624              * weights so that low prio queue from higher class
0625              * gets more requests than high prio queue from lower
0626              * class.
0627              */
0628             wsum = 0;
0629             for (i = 0; i <= class_idx; i++) {
0630                 wsum = wsum * IOPRIO_BE_NR +
0631                     sched_data->service_tree[i].wsum;
0632             }
0633         }
0634         limit = DIV_ROUND_CLOSEST(limit * entity->weight, wsum);
0635         if (entity->allocated >= limit) {
0636             bfq_log_bfqq(bfqq->bfqd, bfqq,
0637                 "too many requests: allocated %d limit %d level %d",
0638                 entity->allocated, limit, level);
0639             ret = true;
0640             break;
0641         }
0642     }
0643 out:
0644     spin_unlock_irq(&bfqd->lock);
0645     if (entities != inline_entities)
0646         kfree(entities);
0647     return ret;
0648 }
0649 #else
0650 static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
0651 {
0652     return false;
0653 }
0654 #endif
0655 
0656 /*
0657  * Async I/O can easily starve sync I/O (both sync reads and sync
0658  * writes), by consuming all tags. Similarly, storms of sync writes,
0659  * such as those that sync(2) may trigger, can starve sync reads.
0660  * Limit depths of async I/O and sync writes so as to counter both
0661  * problems.
0662  *
0663  * Also if a bfq queue or its parent cgroup consume more tags than would be
0664  * appropriate for their weight, we trim the available tag depth to 1. This
0665  * avoids a situation where one cgroup can starve another cgroup from tags and
0666  * thus block service differentiation among cgroups. Note that because the
0667  * queue / cgroup already has many requests allocated and queued, this does not
0668  * significantly affect service guarantees coming from the BFQ scheduling
0669  * algorithm.
0670  */
0671 static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
0672 {
0673     struct bfq_data *bfqd = data->q->elevator->elevator_data;
0674     struct bfq_io_cq *bic = bfq_bic_lookup(data->q);
0675     struct bfq_queue *bfqq = bic ? bic_to_bfqq(bic, op_is_sync(opf)) : NULL;
0676     int depth;
0677     unsigned limit = data->q->nr_requests;
0678 
0679     /* Sync reads have full depth available */
0680     if (op_is_sync(opf) && !op_is_write(opf)) {
0681         depth = 0;
0682     } else {
0683         depth = bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(opf)];
0684         limit = (limit * depth) >> bfqd->full_depth_shift;
0685     }
0686 
0687     /*
0688      * Does queue (or any parent entity) exceed number of requests that
0689      * should be available to it? Heavily limit depth so that it cannot
0690      * consume more available requests and thus starve other entities.
0691      */
0692     if (bfqq && bfqq_request_over_limit(bfqq, limit))
0693         depth = 1;
0694 
0695     bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
0696         __func__, bfqd->wr_busy_queues, op_is_sync(opf), depth);
0697     if (depth)
0698         data->shallow_depth = depth;
0699 }
0700 
0701 static struct bfq_queue *
0702 bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
0703              sector_t sector, struct rb_node **ret_parent,
0704              struct rb_node ***rb_link)
0705 {
0706     struct rb_node **p, *parent;
0707     struct bfq_queue *bfqq = NULL;
0708 
0709     parent = NULL;
0710     p = &root->rb_node;
0711     while (*p) {
0712         struct rb_node **n;
0713 
0714         parent = *p;
0715         bfqq = rb_entry(parent, struct bfq_queue, pos_node);
0716 
0717         /*
0718          * Sort strictly based on sector. Smallest to the left,
0719          * largest to the right.
0720          */
0721         if (sector > blk_rq_pos(bfqq->next_rq))
0722             n = &(*p)->rb_right;
0723         else if (sector < blk_rq_pos(bfqq->next_rq))
0724             n = &(*p)->rb_left;
0725         else
0726             break;
0727         p = n;
0728         bfqq = NULL;
0729     }
0730 
0731     *ret_parent = parent;
0732     if (rb_link)
0733         *rb_link = p;
0734 
0735     bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
0736         (unsigned long long)sector,
0737         bfqq ? bfqq->pid : 0);
0738 
0739     return bfqq;
0740 }
0741 
0742 static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
0743 {
0744     return bfqq->service_from_backlogged > 0 &&
0745         time_is_before_jiffies(bfqq->first_IO_time +
0746                        bfq_merge_time_limit);
0747 }
0748 
0749 /*
0750  * The following function is not marked as __cold because it is
0751  * actually cold, but for the same performance goal described in the
0752  * comments on the likely() at the beginning of
0753  * bfq_setup_cooperator(). Unexpectedly, to reach an even lower
0754  * execution time for the case where this function is not invoked, we
0755  * had to add an unlikely() in each involved if().
0756  */
0757 void __cold
0758 bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
0759 {
0760     struct rb_node **p, *parent;
0761     struct bfq_queue *__bfqq;
0762 
0763     if (bfqq->pos_root) {
0764         rb_erase(&bfqq->pos_node, bfqq->pos_root);
0765         bfqq->pos_root = NULL;
0766     }
0767 
0768     /* oom_bfqq does not participate in queue merging */
0769     if (bfqq == &bfqd->oom_bfqq)
0770         return;
0771 
0772     /*
0773      * bfqq cannot be merged any longer (see comments in
0774      * bfq_setup_cooperator): no point in adding bfqq into the
0775      * position tree.
0776      */
0777     if (bfq_too_late_for_merging(bfqq))
0778         return;
0779 
0780     if (bfq_class_idle(bfqq))
0781         return;
0782     if (!bfqq->next_rq)
0783         return;
0784 
0785     bfqq->pos_root = &bfqq_group(bfqq)->rq_pos_tree;
0786     __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
0787             blk_rq_pos(bfqq->next_rq), &parent, &p);
0788     if (!__bfqq) {
0789         rb_link_node(&bfqq->pos_node, parent, p);
0790         rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
0791     } else
0792         bfqq->pos_root = NULL;
0793 }
0794 
0795 /*
0796  * The following function returns false either if every active queue
0797  * must receive the same share of the throughput (symmetric scenario),
0798  * or, as a special case, if bfqq must receive a share of the
0799  * throughput lower than or equal to the share that every other active
0800  * queue must receive.  If bfqq does sync I/O, then these are the only
0801  * two cases where bfqq happens to be guaranteed its share of the
0802  * throughput even if I/O dispatching is not plugged when bfqq remains
0803  * temporarily empty (for more details, see the comments in the
0804  * function bfq_better_to_idle()). For this reason, the return value
0805  * of this function is used to check whether I/O-dispatch plugging can
0806  * be avoided.
0807  *
0808  * The above first case (symmetric scenario) occurs when:
0809  * 1) all active queues have the same weight,
0810  * 2) all active queues belong to the same I/O-priority class,
0811  * 3) all active groups at the same level in the groups tree have the same
0812  *    weight,
0813  * 4) all active groups at the same level in the groups tree have the same
0814  *    number of children.
0815  *
0816  * Unfortunately, keeping the necessary state for evaluating exactly
0817  * the last two symmetry sub-conditions above would be quite complex
0818  * and time consuming. Therefore this function evaluates, instead,
0819  * only the following stronger three sub-conditions, for which it is
0820  * much easier to maintain the needed state:
0821  * 1) all active queues have the same weight,
0822  * 2) all active queues belong to the same I/O-priority class,
0823  * 3) there are no active groups.
0824  * In particular, the last condition is always true if hierarchical
0825  * support or the cgroups interface are not enabled, thus no state
0826  * needs to be maintained in this case.
0827  */
0828 static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
0829                    struct bfq_queue *bfqq)
0830 {
0831     bool smallest_weight = bfqq &&
0832         bfqq->weight_counter &&
0833         bfqq->weight_counter ==
0834         container_of(
0835             rb_first_cached(&bfqd->queue_weights_tree),
0836             struct bfq_weight_counter,
0837             weights_node);
0838 
0839     /*
0840      * For queue weights to differ, queue_weights_tree must contain
0841      * at least two nodes.
0842      */
0843     bool varied_queue_weights = !smallest_weight &&
0844         !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
0845         (bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
0846          bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
0847 
0848     bool multiple_classes_busy =
0849         (bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
0850         (bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
0851         (bfqd->busy_queues[1] && bfqd->busy_queues[2]);
0852 
0853     return varied_queue_weights || multiple_classes_busy
0854 #ifdef CONFIG_BFQ_GROUP_IOSCHED
0855            || bfqd->num_groups_with_pending_reqs > 0
0856 #endif
0857         ;
0858 }
0859 
0860 /*
0861  * If the weight-counter tree passed as input contains no counter for
0862  * the weight of the input queue, then add that counter; otherwise just
0863  * increment the existing counter.
0864  *
0865  * Note that weight-counter trees contain few nodes in mostly symmetric
0866  * scenarios. For example, if all queues have the same weight, then the
0867  * weight-counter tree for the queues may contain at most one node.
0868  * This holds even if low_latency is on, because weight-raised queues
0869  * are not inserted in the tree.
0870  * In most scenarios, the rate at which nodes are created/destroyed
0871  * should be low too.
0872  */
0873 void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
0874               struct rb_root_cached *root)
0875 {
0876     struct bfq_entity *entity = &bfqq->entity;
0877     struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
0878     bool leftmost = true;
0879 
0880     /*
0881      * Do not insert if the queue is already associated with a
0882      * counter, which happens if:
0883      *   1) a request arrival has caused the queue to become both
0884      *      non-weight-raised, and hence change its weight, and
0885      *      backlogged; in this respect, each of the two events
0886      *      causes an invocation of this function,
0887      *   2) this is the invocation of this function caused by the
0888      *      second event. This second invocation is actually useless,
0889      *      and we handle this fact by exiting immediately. More
0890      *      efficient or clearer solutions might possibly be adopted.
0891      */
0892     if (bfqq->weight_counter)
0893         return;
0894 
0895     while (*new) {
0896         struct bfq_weight_counter *__counter = container_of(*new,
0897                         struct bfq_weight_counter,
0898                         weights_node);
0899         parent = *new;
0900 
0901         if (entity->weight == __counter->weight) {
0902             bfqq->weight_counter = __counter;
0903             goto inc_counter;
0904         }
0905         if (entity->weight < __counter->weight)
0906             new = &((*new)->rb_left);
0907         else {
0908             new = &((*new)->rb_right);
0909             leftmost = false;
0910         }
0911     }
0912 
0913     bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
0914                        GFP_ATOMIC);
0915 
0916     /*
0917      * In the unlucky event of an allocation failure, we just
0918      * exit. This will cause the weight of queue to not be
0919      * considered in bfq_asymmetric_scenario, which, in its turn,
0920      * causes the scenario to be deemed wrongly symmetric in case
0921      * bfqq's weight would have been the only weight making the
0922      * scenario asymmetric.  On the bright side, no unbalance will
0923      * however occur when bfqq becomes inactive again (the
0924      * invocation of this function is triggered by an activation
0925      * of queue).  In fact, bfq_weights_tree_remove does nothing
0926      * if !bfqq->weight_counter.
0927      */
0928     if (unlikely(!bfqq->weight_counter))
0929         return;
0930 
0931     bfqq->weight_counter->weight = entity->weight;
0932     rb_link_node(&bfqq->weight_counter->weights_node, parent, new);
0933     rb_insert_color_cached(&bfqq->weight_counter->weights_node, root,
0934                 leftmost);
0935 
0936 inc_counter:
0937     bfqq->weight_counter->num_active++;
0938     bfqq->ref++;
0939 }
0940 
0941 /*
0942  * Decrement the weight counter associated with the queue, and, if the
0943  * counter reaches 0, remove the counter from the tree.
0944  * See the comments to the function bfq_weights_tree_add() for considerations
0945  * about overhead.
0946  */
0947 void __bfq_weights_tree_remove(struct bfq_data *bfqd,
0948                    struct bfq_queue *bfqq,
0949                    struct rb_root_cached *root)
0950 {
0951     if (!bfqq->weight_counter)
0952         return;
0953 
0954     bfqq->weight_counter->num_active--;
0955     if (bfqq->weight_counter->num_active > 0)
0956         goto reset_entity_pointer;
0957 
0958     rb_erase_cached(&bfqq->weight_counter->weights_node, root);
0959     kfree(bfqq->weight_counter);
0960 
0961 reset_entity_pointer:
0962     bfqq->weight_counter = NULL;
0963     bfq_put_queue(bfqq);
0964 }
0965 
0966 /*
0967  * Invoke __bfq_weights_tree_remove on bfqq and decrement the number
0968  * of active groups for each queue's inactive parent entity.
0969  */
0970 void bfq_weights_tree_remove(struct bfq_data *bfqd,
0971                  struct bfq_queue *bfqq)
0972 {
0973     struct bfq_entity *entity = bfqq->entity.parent;
0974 
0975     for_each_entity(entity) {
0976         struct bfq_sched_data *sd = entity->my_sched_data;
0977 
0978         if (sd->next_in_service || sd->in_service_entity) {
0979             /*
0980              * entity is still active, because either
0981              * next_in_service or in_service_entity is not
0982              * NULL (see the comments on the definition of
0983              * next_in_service for details on why
0984              * in_service_entity must be checked too).
0985              *
0986              * As a consequence, its parent entities are
0987              * active as well, and thus this loop must
0988              * stop here.
0989              */
0990             break;
0991         }
0992 
0993         /*
0994          * The decrement of num_groups_with_pending_reqs is
0995          * not performed immediately upon the deactivation of
0996          * entity, but it is delayed to when it also happens
0997          * that the first leaf descendant bfqq of entity gets
0998          * all its pending requests completed. The following
0999          * instructions perform this delayed decrement, if
1000          * needed. See the comments on
1001          * num_groups_with_pending_reqs for details.
1002          */
1003         if (entity->in_groups_with_pending_reqs) {
1004             entity->in_groups_with_pending_reqs = false;
1005             bfqd->num_groups_with_pending_reqs--;
1006         }
1007     }
1008 
1009     /*
1010      * Next function is invoked last, because it causes bfqq to be
1011      * freed if the following holds: bfqq is not in service and
1012      * has no dispatched request. DO NOT use bfqq after the next
1013      * function invocation.
1014      */
1015     __bfq_weights_tree_remove(bfqd, bfqq,
1016                   &bfqd->queue_weights_tree);
1017 }
1018 
1019 /*
1020  * Return expired entry, or NULL to just start from scratch in rbtree.
1021  */
1022 static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
1023                       struct request *last)
1024 {
1025     struct request *rq;
1026 
1027     if (bfq_bfqq_fifo_expire(bfqq))
1028         return NULL;
1029 
1030     bfq_mark_bfqq_fifo_expire(bfqq);
1031 
1032     rq = rq_entry_fifo(bfqq->fifo.next);
1033 
1034     if (rq == last || ktime_get_ns() < rq->fifo_time)
1035         return NULL;
1036 
1037     bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
1038     return rq;
1039 }
1040 
1041 static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
1042                     struct bfq_queue *bfqq,
1043                     struct request *last)
1044 {
1045     struct rb_node *rbnext = rb_next(&last->rb_node);
1046     struct rb_node *rbprev = rb_prev(&last->rb_node);
1047     struct request *next, *prev = NULL;
1048 
1049     /* Follow expired path, else get first next available. */
1050     next = bfq_check_fifo(bfqq, last);
1051     if (next)
1052         return next;
1053 
1054     if (rbprev)
1055         prev = rb_entry_rq(rbprev);
1056 
1057     if (rbnext)
1058         next = rb_entry_rq(rbnext);
1059     else {
1060         rbnext = rb_first(&bfqq->sort_list);
1061         if (rbnext && rbnext != &last->rb_node)
1062             next = rb_entry_rq(rbnext);
1063     }
1064 
1065     return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
1066 }
1067 
1068 /* see the definition of bfq_async_charge_factor for details */
1069 static unsigned long bfq_serv_to_charge(struct request *rq,
1070                     struct bfq_queue *bfqq)
1071 {
1072     if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
1073         bfq_asymmetric_scenario(bfqq->bfqd, bfqq))
1074         return blk_rq_sectors(rq);
1075 
1076     return blk_rq_sectors(rq) * bfq_async_charge_factor;
1077 }
1078 
1079 /**
1080  * bfq_updated_next_req - update the queue after a new next_rq selection.
1081  * @bfqd: the device data the queue belongs to.
1082  * @bfqq: the queue to update.
1083  *
1084  * If the first request of a queue changes we make sure that the queue
1085  * has enough budget to serve at least its first request (if the
1086  * request has grown).  We do this because if the queue has not enough
1087  * budget for its first request, it has to go through two dispatch
1088  * rounds to actually get it dispatched.
1089  */
1090 static void bfq_updated_next_req(struct bfq_data *bfqd,
1091                  struct bfq_queue *bfqq)
1092 {
1093     struct bfq_entity *entity = &bfqq->entity;
1094     struct request *next_rq = bfqq->next_rq;
1095     unsigned long new_budget;
1096 
1097     if (!next_rq)
1098         return;
1099 
1100     if (bfqq == bfqd->in_service_queue)
1101         /*
1102          * In order not to break guarantees, budgets cannot be
1103          * changed after an entity has been selected.
1104          */
1105         return;
1106 
1107     new_budget = max_t(unsigned long,
1108                max_t(unsigned long, bfqq->max_budget,
1109                  bfq_serv_to_charge(next_rq, bfqq)),
1110                entity->service);
1111     if (entity->budget != new_budget) {
1112         entity->budget = new_budget;
1113         bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
1114                      new_budget);
1115         bfq_requeue_bfqq(bfqd, bfqq, false);
1116     }
1117 }
1118 
1119 static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
1120 {
1121     u64 dur;
1122 
1123     if (bfqd->bfq_wr_max_time > 0)
1124         return bfqd->bfq_wr_max_time;
1125 
1126     dur = bfqd->rate_dur_prod;
1127     do_div(dur, bfqd->peak_rate);
1128 
1129     /*
1130      * Limit duration between 3 and 25 seconds. The upper limit
1131      * has been conservatively set after the following worst case:
1132      * on a QEMU/KVM virtual machine
1133      * - running in a slow PC
1134      * - with a virtual disk stacked on a slow low-end 5400rpm HDD
1135      * - serving a heavy I/O workload, such as the sequential reading
1136      *   of several files
1137      * mplayer took 23 seconds to start, if constantly weight-raised.
1138      *
1139      * As for higher values than that accommodating the above bad
1140      * scenario, tests show that higher values would often yield
1141      * the opposite of the desired result, i.e., would worsen
1142      * responsiveness by allowing non-interactive applications to
1143      * preserve weight raising for too long.
1144      *
1145      * On the other end, lower values than 3 seconds make it
1146      * difficult for most interactive tasks to complete their jobs
1147      * before weight-raising finishes.
1148      */
1149     return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
1150 }
1151 
1152 /* switch back from soft real-time to interactive weight raising */
1153 static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1154                       struct bfq_data *bfqd)
1155 {
1156     bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1157     bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1158     bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1159 }
1160 
1161 static void
1162 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1163               struct bfq_io_cq *bic, bool bfq_already_existing)
1164 {
1165     unsigned int old_wr_coeff = 1;
1166     bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1167 
1168     if (bic->saved_has_short_ttime)
1169         bfq_mark_bfqq_has_short_ttime(bfqq);
1170     else
1171         bfq_clear_bfqq_has_short_ttime(bfqq);
1172 
1173     if (bic->saved_IO_bound)
1174         bfq_mark_bfqq_IO_bound(bfqq);
1175     else
1176         bfq_clear_bfqq_IO_bound(bfqq);
1177 
1178     bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns;
1179     bfqq->inject_limit = bic->saved_inject_limit;
1180     bfqq->decrease_time_jif = bic->saved_decrease_time_jif;
1181 
1182     bfqq->entity.new_weight = bic->saved_weight;
1183     bfqq->ttime = bic->saved_ttime;
1184     bfqq->io_start_time = bic->saved_io_start_time;
1185     bfqq->tot_idle_time = bic->saved_tot_idle_time;
1186     /*
1187      * Restore weight coefficient only if low_latency is on
1188      */
1189     if (bfqd->low_latency) {
1190         old_wr_coeff = bfqq->wr_coeff;
1191         bfqq->wr_coeff = bic->saved_wr_coeff;
1192     }
1193     bfqq->service_from_wr = bic->saved_service_from_wr;
1194     bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
1195     bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
1196     bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
1197 
1198     if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1199         time_is_before_jiffies(bfqq->last_wr_start_finish +
1200                    bfqq->wr_cur_max_time))) {
1201         if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1202             !bfq_bfqq_in_large_burst(bfqq) &&
1203             time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1204                          bfq_wr_duration(bfqd))) {
1205             switch_back_to_interactive_wr(bfqq, bfqd);
1206         } else {
1207             bfqq->wr_coeff = 1;
1208             bfq_log_bfqq(bfqq->bfqd, bfqq,
1209                      "resume state: switching off wr");
1210         }
1211     }
1212 
1213     /* make sure weight will be updated, however we got here */
1214     bfqq->entity.prio_changed = 1;
1215 
1216     if (likely(!busy))
1217         return;
1218 
1219     if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1220         bfqd->wr_busy_queues++;
1221     else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1222         bfqd->wr_busy_queues--;
1223 }
1224 
1225 static int bfqq_process_refs(struct bfq_queue *bfqq)
1226 {
1227     return bfqq->ref - bfqq->entity.allocated -
1228         bfqq->entity.on_st_or_in_serv -
1229         (bfqq->weight_counter != NULL) - bfqq->stable_ref;
1230 }
1231 
1232 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
1233 static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1234 {
1235     struct bfq_queue *item;
1236     struct hlist_node *n;
1237 
1238     hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1239         hlist_del_init(&item->burst_list_node);
1240 
1241     /*
1242      * Start the creation of a new burst list only if there is no
1243      * active queue. See comments on the conditional invocation of
1244      * bfq_handle_burst().
1245      */
1246     if (bfq_tot_busy_queues(bfqd) == 0) {
1247         hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1248         bfqd->burst_size = 1;
1249     } else
1250         bfqd->burst_size = 0;
1251 
1252     bfqd->burst_parent_entity = bfqq->entity.parent;
1253 }
1254 
1255 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1256 static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1257 {
1258     /* Increment burst size to take into account also bfqq */
1259     bfqd->burst_size++;
1260 
1261     if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1262         struct bfq_queue *pos, *bfqq_item;
1263         struct hlist_node *n;
1264 
1265         /*
1266          * Enough queues have been activated shortly after each
1267          * other to consider this burst as large.
1268          */
1269         bfqd->large_burst = true;
1270 
1271         /*
1272          * We can now mark all queues in the burst list as
1273          * belonging to a large burst.
1274          */
1275         hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1276                      burst_list_node)
1277             bfq_mark_bfqq_in_large_burst(bfqq_item);
1278         bfq_mark_bfqq_in_large_burst(bfqq);
1279 
1280         /*
1281          * From now on, and until the current burst finishes, any
1282          * new queue being activated shortly after the last queue
1283          * was inserted in the burst can be immediately marked as
1284          * belonging to a large burst. So the burst list is not
1285          * needed any more. Remove it.
1286          */
1287         hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1288                       burst_list_node)
1289             hlist_del_init(&pos->burst_list_node);
1290     } else /*
1291         * Burst not yet large: add bfqq to the burst list. Do
1292         * not increment the ref counter for bfqq, because bfqq
1293         * is removed from the burst list before freeing bfqq
1294         * in put_queue.
1295         */
1296         hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1297 }
1298 
1299 /*
1300  * If many queues belonging to the same group happen to be created
1301  * shortly after each other, then the processes associated with these
1302  * queues have typically a common goal. In particular, bursts of queue
1303  * creations are usually caused by services or applications that spawn
1304  * many parallel threads/processes. Examples are systemd during boot,
1305  * or git grep. To help these processes get their job done as soon as
1306  * possible, it is usually better to not grant either weight-raising
1307  * or device idling to their queues, unless these queues must be
1308  * protected from the I/O flowing through other active queues.
1309  *
1310  * In this comment we describe, firstly, the reasons why this fact
1311  * holds, and, secondly, the next function, which implements the main
1312  * steps needed to properly mark these queues so that they can then be
1313  * treated in a different way.
1314  *
1315  * The above services or applications benefit mostly from a high
1316  * throughput: the quicker the requests of the activated queues are
1317  * cumulatively served, the sooner the target job of these queues gets
1318  * completed. As a consequence, weight-raising any of these queues,
1319  * which also implies idling the device for it, is almost always
1320  * counterproductive, unless there are other active queues to isolate
1321  * these new queues from. If there no other active queues, then
1322  * weight-raising these new queues just lowers throughput in most
1323  * cases.
1324  *
1325  * On the other hand, a burst of queue creations may be caused also by
1326  * the start of an application that does not consist of a lot of
1327  * parallel I/O-bound threads. In fact, with a complex application,
1328  * several short processes may need to be executed to start-up the
1329  * application. In this respect, to start an application as quickly as
1330  * possible, the best thing to do is in any case to privilege the I/O
1331  * related to the application with respect to all other
1332  * I/O. Therefore, the best strategy to start as quickly as possible
1333  * an application that causes a burst of queue creations is to
1334  * weight-raise all the queues created during the burst. This is the
1335  * exact opposite of the best strategy for the other type of bursts.
1336  *
1337  * In the end, to take the best action for each of the two cases, the
1338  * two types of bursts need to be distinguished. Fortunately, this
1339  * seems relatively easy, by looking at the sizes of the bursts. In
1340  * particular, we found a threshold such that only bursts with a
1341  * larger size than that threshold are apparently caused by
1342  * services or commands such as systemd or git grep. For brevity,
1343  * hereafter we call just 'large' these bursts. BFQ *does not*
1344  * weight-raise queues whose creation occurs in a large burst. In
1345  * addition, for each of these queues BFQ performs or does not perform
1346  * idling depending on which choice boosts the throughput more. The
1347  * exact choice depends on the device and request pattern at
1348  * hand.
1349  *
1350  * Unfortunately, false positives may occur while an interactive task
1351  * is starting (e.g., an application is being started). The
1352  * consequence is that the queues associated with the task do not
1353  * enjoy weight raising as expected. Fortunately these false positives
1354  * are very rare. They typically occur if some service happens to
1355  * start doing I/O exactly when the interactive task starts.
1356  *
1357  * Turning back to the next function, it is invoked only if there are
1358  * no active queues (apart from active queues that would belong to the
1359  * same, possible burst bfqq would belong to), and it implements all
1360  * the steps needed to detect the occurrence of a large burst and to
1361  * properly mark all the queues belonging to it (so that they can then
1362  * be treated in a different way). This goal is achieved by
1363  * maintaining a "burst list" that holds, temporarily, the queues that
1364  * belong to the burst in progress. The list is then used to mark
1365  * these queues as belonging to a large burst if the burst does become
1366  * large. The main steps are the following.
1367  *
1368  * . when the very first queue is created, the queue is inserted into the
1369  *   list (as it could be the first queue in a possible burst)
1370  *
1371  * . if the current burst has not yet become large, and a queue Q that does
1372  *   not yet belong to the burst is activated shortly after the last time
1373  *   at which a new queue entered the burst list, then the function appends
1374  *   Q to the burst list
1375  *
1376  * . if, as a consequence of the previous step, the burst size reaches
1377  *   the large-burst threshold, then
1378  *
1379  *     . all the queues in the burst list are marked as belonging to a
1380  *       large burst
1381  *
1382  *     . the burst list is deleted; in fact, the burst list already served
1383  *       its purpose (keeping temporarily track of the queues in a burst,
1384  *       so as to be able to mark them as belonging to a large burst in the
1385  *       previous sub-step), and now is not needed any more
1386  *
1387  *     . the device enters a large-burst mode
1388  *
1389  * . if a queue Q that does not belong to the burst is created while
1390  *   the device is in large-burst mode and shortly after the last time
1391  *   at which a queue either entered the burst list or was marked as
1392  *   belonging to the current large burst, then Q is immediately marked
1393  *   as belonging to a large burst.
1394  *
1395  * . if a queue Q that does not belong to the burst is created a while
1396  *   later, i.e., not shortly after, than the last time at which a queue
1397  *   either entered the burst list or was marked as belonging to the
1398  *   current large burst, then the current burst is deemed as finished and:
1399  *
1400  *        . the large-burst mode is reset if set
1401  *
1402  *        . the burst list is emptied
1403  *
1404  *        . Q is inserted in the burst list, as Q may be the first queue
1405  *          in a possible new burst (then the burst list contains just Q
1406  *          after this step).
1407  */
1408 static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1409 {
1410     /*
1411      * If bfqq is already in the burst list or is part of a large
1412      * burst, or finally has just been split, then there is
1413      * nothing else to do.
1414      */
1415     if (!hlist_unhashed(&bfqq->burst_list_node) ||
1416         bfq_bfqq_in_large_burst(bfqq) ||
1417         time_is_after_eq_jiffies(bfqq->split_time +
1418                      msecs_to_jiffies(10)))
1419         return;
1420 
1421     /*
1422      * If bfqq's creation happens late enough, or bfqq belongs to
1423      * a different group than the burst group, then the current
1424      * burst is finished, and related data structures must be
1425      * reset.
1426      *
1427      * In this respect, consider the special case where bfqq is
1428      * the very first queue created after BFQ is selected for this
1429      * device. In this case, last_ins_in_burst and
1430      * burst_parent_entity are not yet significant when we get
1431      * here. But it is easy to verify that, whether or not the
1432      * following condition is true, bfqq will end up being
1433      * inserted into the burst list. In particular the list will
1434      * happen to contain only bfqq. And this is exactly what has
1435      * to happen, as bfqq may be the first queue of the first
1436      * burst.
1437      */
1438     if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1439         bfqd->bfq_burst_interval) ||
1440         bfqq->entity.parent != bfqd->burst_parent_entity) {
1441         bfqd->large_burst = false;
1442         bfq_reset_burst_list(bfqd, bfqq);
1443         goto end;
1444     }
1445 
1446     /*
1447      * If we get here, then bfqq is being activated shortly after the
1448      * last queue. So, if the current burst is also large, we can mark
1449      * bfqq as belonging to this large burst immediately.
1450      */
1451     if (bfqd->large_burst) {
1452         bfq_mark_bfqq_in_large_burst(bfqq);
1453         goto end;
1454     }
1455 
1456     /*
1457      * If we get here, then a large-burst state has not yet been
1458      * reached, but bfqq is being activated shortly after the last
1459      * queue. Then we add bfqq to the burst.
1460      */
1461     bfq_add_to_burst(bfqd, bfqq);
1462 end:
1463     /*
1464      * At this point, bfqq either has been added to the current
1465      * burst or has caused the current burst to terminate and a
1466      * possible new burst to start. In particular, in the second
1467      * case, bfqq has become the first queue in the possible new
1468      * burst.  In both cases last_ins_in_burst needs to be moved
1469      * forward.
1470      */
1471     bfqd->last_ins_in_burst = jiffies;
1472 }
1473 
1474 static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1475 {
1476     struct bfq_entity *entity = &bfqq->entity;
1477 
1478     return entity->budget - entity->service;
1479 }
1480 
1481 /*
1482  * If enough samples have been computed, return the current max budget
1483  * stored in bfqd, which is dynamically updated according to the
1484  * estimated disk peak rate; otherwise return the default max budget
1485  */
1486 static int bfq_max_budget(struct bfq_data *bfqd)
1487 {
1488     if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1489         return bfq_default_max_budget;
1490     else
1491         return bfqd->bfq_max_budget;
1492 }
1493 
1494 /*
1495  * Return min budget, which is a fraction of the current or default
1496  * max budget (trying with 1/32)
1497  */
1498 static int bfq_min_budget(struct bfq_data *bfqd)
1499 {
1500     if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1501         return bfq_default_max_budget / 32;
1502     else
1503         return bfqd->bfq_max_budget / 32;
1504 }
1505 
1506 /*
1507  * The next function, invoked after the input queue bfqq switches from
1508  * idle to busy, updates the budget of bfqq. The function also tells
1509  * whether the in-service queue should be expired, by returning
1510  * true. The purpose of expiring the in-service queue is to give bfqq
1511  * the chance to possibly preempt the in-service queue, and the reason
1512  * for preempting the in-service queue is to achieve one of the two
1513  * goals below.
1514  *
1515  * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1516  * expired because it has remained idle. In particular, bfqq may have
1517  * expired for one of the following two reasons:
1518  *
1519  * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1520  *   and did not make it to issue a new request before its last
1521  *   request was served;
1522  *
1523  * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1524  *   a new request before the expiration of the idling-time.
1525  *
1526  * Even if bfqq has expired for one of the above reasons, the process
1527  * associated with the queue may be however issuing requests greedily,
1528  * and thus be sensitive to the bandwidth it receives (bfqq may have
1529  * remained idle for other reasons: CPU high load, bfqq not enjoying
1530  * idling, I/O throttling somewhere in the path from the process to
1531  * the I/O scheduler, ...). But if, after every expiration for one of
1532  * the above two reasons, bfqq has to wait for the service of at least
1533  * one full budget of another queue before being served again, then
1534  * bfqq is likely to get a much lower bandwidth or resource time than
1535  * its reserved ones. To address this issue, two countermeasures need
1536  * to be taken.
1537  *
1538  * First, the budget and the timestamps of bfqq need to be updated in
1539  * a special way on bfqq reactivation: they need to be updated as if
1540  * bfqq did not remain idle and did not expire. In fact, if they are
1541  * computed as if bfqq expired and remained idle until reactivation,
1542  * then the process associated with bfqq is treated as if, instead of
1543  * being greedy, it stopped issuing requests when bfqq remained idle,
1544  * and restarts issuing requests only on this reactivation. In other
1545  * words, the scheduler does not help the process recover the "service
1546  * hole" between bfqq expiration and reactivation. As a consequence,
1547  * the process receives a lower bandwidth than its reserved one. In
1548  * contrast, to recover this hole, the budget must be updated as if
1549  * bfqq was not expired at all before this reactivation, i.e., it must
1550  * be set to the value of the remaining budget when bfqq was
1551  * expired. Along the same line, timestamps need to be assigned the
1552  * value they had the last time bfqq was selected for service, i.e.,
1553  * before last expiration. Thus timestamps need to be back-shifted
1554  * with respect to their normal computation (see [1] for more details
1555  * on this tricky aspect).
1556  *
1557  * Secondly, to allow the process to recover the hole, the in-service
1558  * queue must be expired too, to give bfqq the chance to preempt it
1559  * immediately. In fact, if bfqq has to wait for a full budget of the
1560  * in-service queue to be completed, then it may become impossible to
1561  * let the process recover the hole, even if the back-shifted
1562  * timestamps of bfqq are lower than those of the in-service queue. If
1563  * this happens for most or all of the holes, then the process may not
1564  * receive its reserved bandwidth. In this respect, it is worth noting
1565  * that, being the service of outstanding requests unpreemptible, a
1566  * little fraction of the holes may however be unrecoverable, thereby
1567  * causing a little loss of bandwidth.
1568  *
1569  * The last important point is detecting whether bfqq does need this
1570  * bandwidth recovery. In this respect, the next function deems the
1571  * process associated with bfqq greedy, and thus allows it to recover
1572  * the hole, if: 1) the process is waiting for the arrival of a new
1573  * request (which implies that bfqq expired for one of the above two
1574  * reasons), and 2) such a request has arrived soon. The first
1575  * condition is controlled through the flag non_blocking_wait_rq,
1576  * while the second through the flag arrived_in_time. If both
1577  * conditions hold, then the function computes the budget in the
1578  * above-described special way, and signals that the in-service queue
1579  * should be expired. Timestamp back-shifting is done later in
1580  * __bfq_activate_entity.
1581  *
1582  * 2. Reduce latency. Even if timestamps are not backshifted to let
1583  * the process associated with bfqq recover a service hole, bfqq may
1584  * however happen to have, after being (re)activated, a lower finish
1585  * timestamp than the in-service queue.  That is, the next budget of
1586  * bfqq may have to be completed before the one of the in-service
1587  * queue. If this is the case, then preempting the in-service queue
1588  * allows this goal to be achieved, apart from the unpreemptible,
1589  * outstanding requests mentioned above.
1590  *
1591  * Unfortunately, regardless of which of the above two goals one wants
1592  * to achieve, service trees need first to be updated to know whether
1593  * the in-service queue must be preempted. To have service trees
1594  * correctly updated, the in-service queue must be expired and
1595  * rescheduled, and bfqq must be scheduled too. This is one of the
1596  * most costly operations (in future versions, the scheduling
1597  * mechanism may be re-designed in such a way to make it possible to
1598  * know whether preemption is needed without needing to update service
1599  * trees). In addition, queue preemptions almost always cause random
1600  * I/O, which may in turn cause loss of throughput. Finally, there may
1601  * even be no in-service queue when the next function is invoked (so,
1602  * no queue to compare timestamps with). Because of these facts, the
1603  * next function adopts the following simple scheme to avoid costly
1604  * operations, too frequent preemptions and too many dependencies on
1605  * the state of the scheduler: it requests the expiration of the
1606  * in-service queue (unconditionally) only for queues that need to
1607  * recover a hole. Then it delegates to other parts of the code the
1608  * responsibility of handling the above case 2.
1609  */
1610 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1611                         struct bfq_queue *bfqq,
1612                         bool arrived_in_time)
1613 {
1614     struct bfq_entity *entity = &bfqq->entity;
1615 
1616     /*
1617      * In the next compound condition, we check also whether there
1618      * is some budget left, because otherwise there is no point in
1619      * trying to go on serving bfqq with this same budget: bfqq
1620      * would be expired immediately after being selected for
1621      * service. This would only cause useless overhead.
1622      */
1623     if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1624         bfq_bfqq_budget_left(bfqq) > 0) {
1625         /*
1626          * We do not clear the flag non_blocking_wait_rq here, as
1627          * the latter is used in bfq_activate_bfqq to signal
1628          * that timestamps need to be back-shifted (and is
1629          * cleared right after).
1630          */
1631 
1632         /*
1633          * In next assignment we rely on that either
1634          * entity->service or entity->budget are not updated
1635          * on expiration if bfqq is empty (see
1636          * __bfq_bfqq_recalc_budget). Thus both quantities
1637          * remain unchanged after such an expiration, and the
1638          * following statement therefore assigns to
1639          * entity->budget the remaining budget on such an
1640          * expiration.
1641          */
1642         entity->budget = min_t(unsigned long,
1643                        bfq_bfqq_budget_left(bfqq),
1644                        bfqq->max_budget);
1645 
1646         /*
1647          * At this point, we have used entity->service to get
1648          * the budget left (needed for updating
1649          * entity->budget). Thus we finally can, and have to,
1650          * reset entity->service. The latter must be reset
1651          * because bfqq would otherwise be charged again for
1652          * the service it has received during its previous
1653          * service slot(s).
1654          */
1655         entity->service = 0;
1656 
1657         return true;
1658     }
1659 
1660     /*
1661      * We can finally complete expiration, by setting service to 0.
1662      */
1663     entity->service = 0;
1664     entity->budget = max_t(unsigned long, bfqq->max_budget,
1665                    bfq_serv_to_charge(bfqq->next_rq, bfqq));
1666     bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1667     return false;
1668 }
1669 
1670 /*
1671  * Return the farthest past time instant according to jiffies
1672  * macros.
1673  */
1674 static unsigned long bfq_smallest_from_now(void)
1675 {
1676     return jiffies - MAX_JIFFY_OFFSET;
1677 }
1678 
1679 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1680                          struct bfq_queue *bfqq,
1681                          unsigned int old_wr_coeff,
1682                          bool wr_or_deserves_wr,
1683                          bool interactive,
1684                          bool in_burst,
1685                          bool soft_rt)
1686 {
1687     if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1688         /* start a weight-raising period */
1689         if (interactive) {
1690             bfqq->service_from_wr = 0;
1691             bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1692             bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1693         } else {
1694             /*
1695              * No interactive weight raising in progress
1696              * here: assign minus infinity to
1697              * wr_start_at_switch_to_srt, to make sure
1698              * that, at the end of the soft-real-time
1699              * weight raising periods that is starting
1700              * now, no interactive weight-raising period
1701              * may be wrongly considered as still in
1702              * progress (and thus actually started by
1703              * mistake).
1704              */
1705             bfqq->wr_start_at_switch_to_srt =
1706                 bfq_smallest_from_now();
1707             bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1708                 BFQ_SOFTRT_WEIGHT_FACTOR;
1709             bfqq->wr_cur_max_time =
1710                 bfqd->bfq_wr_rt_max_time;
1711         }
1712 
1713         /*
1714          * If needed, further reduce budget to make sure it is
1715          * close to bfqq's backlog, so as to reduce the
1716          * scheduling-error component due to a too large
1717          * budget. Do not care about throughput consequences,
1718          * but only about latency. Finally, do not assign a
1719          * too small budget either, to avoid increasing
1720          * latency by causing too frequent expirations.
1721          */
1722         bfqq->entity.budget = min_t(unsigned long,
1723                         bfqq->entity.budget,
1724                         2 * bfq_min_budget(bfqd));
1725     } else if (old_wr_coeff > 1) {
1726         if (interactive) { /* update wr coeff and duration */
1727             bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1728             bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1729         } else if (in_burst)
1730             bfqq->wr_coeff = 1;
1731         else if (soft_rt) {
1732             /*
1733              * The application is now or still meeting the
1734              * requirements for being deemed soft rt.  We
1735              * can then correctly and safely (re)charge
1736              * the weight-raising duration for the
1737              * application with the weight-raising
1738              * duration for soft rt applications.
1739              *
1740              * In particular, doing this recharge now, i.e.,
1741              * before the weight-raising period for the
1742              * application finishes, reduces the probability
1743              * of the following negative scenario:
1744              * 1) the weight of a soft rt application is
1745              *    raised at startup (as for any newly
1746              *    created application),
1747              * 2) since the application is not interactive,
1748              *    at a certain time weight-raising is
1749              *    stopped for the application,
1750              * 3) at that time the application happens to
1751              *    still have pending requests, and hence
1752              *    is destined to not have a chance to be
1753              *    deemed soft rt before these requests are
1754              *    completed (see the comments to the
1755              *    function bfq_bfqq_softrt_next_start()
1756              *    for details on soft rt detection),
1757              * 4) these pending requests experience a high
1758              *    latency because the application is not
1759              *    weight-raised while they are pending.
1760              */
1761             if (bfqq->wr_cur_max_time !=
1762                 bfqd->bfq_wr_rt_max_time) {
1763                 bfqq->wr_start_at_switch_to_srt =
1764                     bfqq->last_wr_start_finish;
1765 
1766                 bfqq->wr_cur_max_time =
1767                     bfqd->bfq_wr_rt_max_time;
1768                 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1769                     BFQ_SOFTRT_WEIGHT_FACTOR;
1770             }
1771             bfqq->last_wr_start_finish = jiffies;
1772         }
1773     }
1774 }
1775 
1776 static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1777                     struct bfq_queue *bfqq)
1778 {
1779     return bfqq->dispatched == 0 &&
1780         time_is_before_jiffies(
1781             bfqq->budget_timeout +
1782             bfqd->bfq_wr_min_idle_time);
1783 }
1784 
1785 
1786 /*
1787  * Return true if bfqq is in a higher priority class, or has a higher
1788  * weight than the in-service queue.
1789  */
1790 static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1791                         struct bfq_queue *in_serv_bfqq)
1792 {
1793     int bfqq_weight, in_serv_weight;
1794 
1795     if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1796         return true;
1797 
1798     if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1799         bfqq_weight = bfqq->entity.weight;
1800         in_serv_weight = in_serv_bfqq->entity.weight;
1801     } else {
1802         if (bfqq->entity.parent)
1803             bfqq_weight = bfqq->entity.parent->weight;
1804         else
1805             bfqq_weight = bfqq->entity.weight;
1806         if (in_serv_bfqq->entity.parent)
1807             in_serv_weight = in_serv_bfqq->entity.parent->weight;
1808         else
1809             in_serv_weight = in_serv_bfqq->entity.weight;
1810     }
1811 
1812     return bfqq_weight > in_serv_weight;
1813 }
1814 
1815 static bool bfq_better_to_idle(struct bfq_queue *bfqq);
1816 
1817 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1818                          struct bfq_queue *bfqq,
1819                          int old_wr_coeff,
1820                          struct request *rq,
1821                          bool *interactive)
1822 {
1823     bool soft_rt, in_burst, wr_or_deserves_wr,
1824         bfqq_wants_to_preempt,
1825         idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1826         /*
1827          * See the comments on
1828          * bfq_bfqq_update_budg_for_activation for
1829          * details on the usage of the next variable.
1830          */
1831         arrived_in_time =  ktime_get_ns() <=
1832             bfqq->ttime.last_end_request +
1833             bfqd->bfq_slice_idle * 3;
1834 
1835 
1836     /*
1837      * bfqq deserves to be weight-raised if:
1838      * - it is sync,
1839      * - it does not belong to a large burst,
1840      * - it has been idle for enough time or is soft real-time,
1841      * - is linked to a bfq_io_cq (it is not shared in any sense),
1842      * - has a default weight (otherwise we assume the user wanted
1843      *   to control its weight explicitly)
1844      */
1845     in_burst = bfq_bfqq_in_large_burst(bfqq);
1846     soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1847         !BFQQ_TOTALLY_SEEKY(bfqq) &&
1848         !in_burst &&
1849         time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1850         bfqq->dispatched == 0 &&
1851         bfqq->entity.new_weight == 40;
1852     *interactive = !in_burst && idle_for_long_time &&
1853         bfqq->entity.new_weight == 40;
1854     /*
1855      * Merged bfq_queues are kept out of weight-raising
1856      * (low-latency) mechanisms. The reason is that these queues
1857      * are usually created for non-interactive and
1858      * non-soft-real-time tasks. Yet this is not the case for
1859      * stably-merged queues. These queues are merged just because
1860      * they are created shortly after each other. So they may
1861      * easily serve the I/O of an interactive or soft-real time
1862      * application, if the application happens to spawn multiple
1863      * processes. So let also stably-merged queued enjoy weight
1864      * raising.
1865      */
1866     wr_or_deserves_wr = bfqd->low_latency &&
1867         (bfqq->wr_coeff > 1 ||
1868          (bfq_bfqq_sync(bfqq) &&
1869           (bfqq->bic || RQ_BIC(rq)->stably_merged) &&
1870            (*interactive || soft_rt)));
1871 
1872     /*
1873      * Using the last flag, update budget and check whether bfqq
1874      * may want to preempt the in-service queue.
1875      */
1876     bfqq_wants_to_preempt =
1877         bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1878                             arrived_in_time);
1879 
1880     /*
1881      * If bfqq happened to be activated in a burst, but has been
1882      * idle for much more than an interactive queue, then we
1883      * assume that, in the overall I/O initiated in the burst, the
1884      * I/O associated with bfqq is finished. So bfqq does not need
1885      * to be treated as a queue belonging to a burst
1886      * anymore. Accordingly, we reset bfqq's in_large_burst flag
1887      * if set, and remove bfqq from the burst list if it's
1888      * there. We do not decrement burst_size, because the fact
1889      * that bfqq does not need to belong to the burst list any
1890      * more does not invalidate the fact that bfqq was created in
1891      * a burst.
1892      */
1893     if (likely(!bfq_bfqq_just_created(bfqq)) &&
1894         idle_for_long_time &&
1895         time_is_before_jiffies(
1896             bfqq->budget_timeout +
1897             msecs_to_jiffies(10000))) {
1898         hlist_del_init(&bfqq->burst_list_node);
1899         bfq_clear_bfqq_in_large_burst(bfqq);
1900     }
1901 
1902     bfq_clear_bfqq_just_created(bfqq);
1903 
1904     if (bfqd->low_latency) {
1905         if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1906             /* wraparound */
1907             bfqq->split_time =
1908                 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1909 
1910         if (time_is_before_jiffies(bfqq->split_time +
1911                        bfqd->bfq_wr_min_idle_time)) {
1912             bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1913                              old_wr_coeff,
1914                              wr_or_deserves_wr,
1915                              *interactive,
1916                              in_burst,
1917                              soft_rt);
1918 
1919             if (old_wr_coeff != bfqq->wr_coeff)
1920                 bfqq->entity.prio_changed = 1;
1921         }
1922     }
1923 
1924     bfqq->last_idle_bklogged = jiffies;
1925     bfqq->service_from_backlogged = 0;
1926     bfq_clear_bfqq_softrt_update(bfqq);
1927 
1928     bfq_add_bfqq_busy(bfqd, bfqq);
1929 
1930     /*
1931      * Expire in-service queue if preemption may be needed for
1932      * guarantees or throughput. As for guarantees, we care
1933      * explicitly about two cases. The first is that bfqq has to
1934      * recover a service hole, as explained in the comments on
1935      * bfq_bfqq_update_budg_for_activation(), i.e., that
1936      * bfqq_wants_to_preempt is true. However, if bfqq does not
1937      * carry time-critical I/O, then bfqq's bandwidth is less
1938      * important than that of queues that carry time-critical I/O.
1939      * So, as a further constraint, we consider this case only if
1940      * bfqq is at least as weight-raised, i.e., at least as time
1941      * critical, as the in-service queue.
1942      *
1943      * The second case is that bfqq is in a higher priority class,
1944      * or has a higher weight than the in-service queue. If this
1945      * condition does not hold, we don't care because, even if
1946      * bfqq does not start to be served immediately, the resulting
1947      * delay for bfqq's I/O is however lower or much lower than
1948      * the ideal completion time to be guaranteed to bfqq's I/O.
1949      *
1950      * In both cases, preemption is needed only if, according to
1951      * the timestamps of both bfqq and of the in-service queue,
1952      * bfqq actually is the next queue to serve. So, to reduce
1953      * useless preemptions, the return value of
1954      * next_queue_may_preempt() is considered in the next compound
1955      * condition too. Yet next_queue_may_preempt() just checks a
1956      * simple, necessary condition for bfqq to be the next queue
1957      * to serve. In fact, to evaluate a sufficient condition, the
1958      * timestamps of the in-service queue would need to be
1959      * updated, and this operation is quite costly (see the
1960      * comments on bfq_bfqq_update_budg_for_activation()).
1961      *
1962      * As for throughput, we ask bfq_better_to_idle() whether we
1963      * still need to plug I/O dispatching. If bfq_better_to_idle()
1964      * says no, then plugging is not needed any longer, either to
1965      * boost throughput or to perserve service guarantees. Then
1966      * the best option is to stop plugging I/O, as not doing so
1967      * would certainly lower throughput. We may end up in this
1968      * case if: (1) upon a dispatch attempt, we detected that it
1969      * was better to plug I/O dispatch, and to wait for a new
1970      * request to arrive for the currently in-service queue, but
1971      * (2) this switch of bfqq to busy changes the scenario.
1972      */
1973     if (bfqd->in_service_queue &&
1974         ((bfqq_wants_to_preempt &&
1975           bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1976          bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue) ||
1977          !bfq_better_to_idle(bfqd->in_service_queue)) &&
1978         next_queue_may_preempt(bfqd))
1979         bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1980                 false, BFQQE_PREEMPTED);
1981 }
1982 
1983 static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1984                    struct bfq_queue *bfqq)
1985 {
1986     /* invalidate baseline total service time */
1987     bfqq->last_serv_time_ns = 0;
1988 
1989     /*
1990      * Reset pointer in case we are waiting for
1991      * some request completion.
1992      */
1993     bfqd->waited_rq = NULL;
1994 
1995     /*
1996      * If bfqq has a short think time, then start by setting the
1997      * inject limit to 0 prudentially, because the service time of
1998      * an injected I/O request may be higher than the think time
1999      * of bfqq, and therefore, if one request was injected when
2000      * bfqq remains empty, this injected request might delay the
2001      * service of the next I/O request for bfqq significantly. In
2002      * case bfqq can actually tolerate some injection, then the
2003      * adaptive update will however raise the limit soon. This
2004      * lucky circumstance holds exactly because bfqq has a short
2005      * think time, and thus, after remaining empty, is likely to
2006      * get new I/O enqueued---and then completed---before being
2007      * expired. This is the very pattern that gives the
2008      * limit-update algorithm the chance to measure the effect of
2009      * injection on request service times, and then to update the
2010      * limit accordingly.
2011      *
2012      * However, in the following special case, the inject limit is
2013      * left to 1 even if the think time is short: bfqq's I/O is
2014      * synchronized with that of some other queue, i.e., bfqq may
2015      * receive new I/O only after the I/O of the other queue is
2016      * completed. Keeping the inject limit to 1 allows the
2017      * blocking I/O to be served while bfqq is in service. And
2018      * this is very convenient both for bfqq and for overall
2019      * throughput, as explained in detail in the comments in
2020      * bfq_update_has_short_ttime().
2021      *
2022      * On the opposite end, if bfqq has a long think time, then
2023      * start directly by 1, because:
2024      * a) on the bright side, keeping at most one request in
2025      * service in the drive is unlikely to cause any harm to the
2026      * latency of bfqq's requests, as the service time of a single
2027      * request is likely to be lower than the think time of bfqq;
2028      * b) on the downside, after becoming empty, bfqq is likely to
2029      * expire before getting its next request. With this request
2030      * arrival pattern, it is very hard to sample total service
2031      * times and update the inject limit accordingly (see comments
2032      * on bfq_update_inject_limit()). So the limit is likely to be
2033      * never, or at least seldom, updated.  As a consequence, by
2034      * setting the limit to 1, we avoid that no injection ever
2035      * occurs with bfqq. On the downside, this proactive step
2036      * further reduces chances to actually compute the baseline
2037      * total service time. Thus it reduces chances to execute the
2038      * limit-update algorithm and possibly raise the limit to more
2039      * than 1.
2040      */
2041     if (bfq_bfqq_has_short_ttime(bfqq))
2042         bfqq->inject_limit = 0;
2043     else
2044         bfqq->inject_limit = 1;
2045 
2046     bfqq->decrease_time_jif = jiffies;
2047 }
2048 
2049 static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
2050 {
2051     u64 tot_io_time = now_ns - bfqq->io_start_time;
2052 
2053     if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
2054         bfqq->tot_idle_time +=
2055             now_ns - bfqq->ttime.last_end_request;
2056 
2057     if (unlikely(bfq_bfqq_just_created(bfqq)))
2058         return;
2059 
2060     /*
2061      * Must be busy for at least about 80% of the time to be
2062      * considered I/O bound.
2063      */
2064     if (bfqq->tot_idle_time * 5 > tot_io_time)
2065         bfq_clear_bfqq_IO_bound(bfqq);
2066     else
2067         bfq_mark_bfqq_IO_bound(bfqq);
2068 
2069     /*
2070      * Keep an observation window of at most 200 ms in the past
2071      * from now.
2072      */
2073     if (tot_io_time > 200 * NSEC_PER_MSEC) {
2074         bfqq->io_start_time = now_ns - (tot_io_time>>1);
2075         bfqq->tot_idle_time >>= 1;
2076     }
2077 }
2078 
2079 /*
2080  * Detect whether bfqq's I/O seems synchronized with that of some
2081  * other queue, i.e., whether bfqq, after remaining empty, happens to
2082  * receive new I/O only right after some I/O request of the other
2083  * queue has been completed. We call waker queue the other queue, and
2084  * we assume, for simplicity, that bfqq may have at most one waker
2085  * queue.
2086  *
2087  * A remarkable throughput boost can be reached by unconditionally
2088  * injecting the I/O of the waker queue, every time a new
2089  * bfq_dispatch_request happens to be invoked while I/O is being
2090  * plugged for bfqq.  In addition to boosting throughput, this
2091  * unblocks bfqq's I/O, thereby improving bandwidth and latency for
2092  * bfqq. Note that these same results may be achieved with the general
2093  * injection mechanism, but less effectively. For details on this
2094  * aspect, see the comments on the choice of the queue for injection
2095  * in bfq_select_queue().
2096  *
2097  * Turning back to the detection of a waker queue, a queue Q is deemed as a
2098  * waker queue for bfqq if, for three consecutive times, bfqq happens to become
2099  * non empty right after a request of Q has been completed within given
2100  * timeout. In this respect, even if bfqq is empty, we do not check for a waker
2101  * if it still has some in-flight I/O. In fact, in this case bfqq is actually
2102  * still being served by the drive, and may receive new I/O on the completion
2103  * of some of the in-flight requests. In particular, on the first time, Q is
2104  * tentatively set as a candidate waker queue, while on the third consecutive
2105  * time that Q is detected, the field waker_bfqq is set to Q, to confirm that Q
2106  * is a waker queue for bfqq. These detection steps are performed only if bfqq
2107  * has a long think time, so as to make it more likely that bfqq's I/O is
2108  * actually being blocked by a synchronization. This last filter, plus the
2109  * above three-times requirement and time limit for detection, make false
2110  * positives less likely.
2111  *
2112  * NOTE
2113  *
2114  * The sooner a waker queue is detected, the sooner throughput can be
2115  * boosted by injecting I/O from the waker queue. Fortunately,
2116  * detection is likely to be actually fast, for the following
2117  * reasons. While blocked by synchronization, bfqq has a long think
2118  * time. This implies that bfqq's inject limit is at least equal to 1
2119  * (see the comments in bfq_update_inject_limit()). So, thanks to
2120  * injection, the waker queue is likely to be served during the very
2121  * first I/O-plugging time interval for bfqq. This triggers the first
2122  * step of the detection mechanism. Thanks again to injection, the
2123  * candidate waker queue is then likely to be confirmed no later than
2124  * during the next I/O-plugging interval for bfqq.
2125  *
2126  * ISSUE
2127  *
2128  * On queue merging all waker information is lost.
2129  */
2130 static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2131                 u64 now_ns)
2132 {
2133     char waker_name[MAX_BFQQ_NAME_LENGTH];
2134 
2135     if (!bfqd->last_completed_rq_bfqq ||
2136         bfqd->last_completed_rq_bfqq == bfqq ||
2137         bfq_bfqq_has_short_ttime(bfqq) ||
2138         now_ns - bfqd->last_completion >= 4 * NSEC_PER_MSEC)
2139         return;
2140 
2141     /*
2142      * We reset waker detection logic also if too much time has passed
2143      * since the first detection. If wakeups are rare, pointless idling
2144      * doesn't hurt throughput that much. The condition below makes sure
2145      * we do not uselessly idle blocking waker in more than 1/64 cases. 
2146      */
2147     if (bfqd->last_completed_rq_bfqq !=
2148         bfqq->tentative_waker_bfqq ||
2149         now_ns > bfqq->waker_detection_started +
2150                     128 * (u64)bfqd->bfq_slice_idle) {
2151         /*
2152          * First synchronization detected with a
2153          * candidate waker queue, or with a different
2154          * candidate waker queue from the current one.
2155          */
2156         bfqq->tentative_waker_bfqq =
2157             bfqd->last_completed_rq_bfqq;
2158         bfqq->num_waker_detections = 1;
2159         bfqq->waker_detection_started = now_ns;
2160         bfq_bfqq_name(bfqq->tentative_waker_bfqq, waker_name,
2161                   MAX_BFQQ_NAME_LENGTH);
2162         bfq_log_bfqq(bfqd, bfqq, "set tentative waker %s", waker_name);
2163     } else /* Same tentative waker queue detected again */
2164         bfqq->num_waker_detections++;
2165 
2166     if (bfqq->num_waker_detections == 3) {
2167         bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
2168         bfqq->tentative_waker_bfqq = NULL;
2169         bfq_bfqq_name(bfqq->waker_bfqq, waker_name,
2170                   MAX_BFQQ_NAME_LENGTH);
2171         bfq_log_bfqq(bfqd, bfqq, "set waker %s", waker_name);
2172 
2173         /*
2174          * If the waker queue disappears, then
2175          * bfqq->waker_bfqq must be reset. To
2176          * this goal, we maintain in each
2177          * waker queue a list, woken_list, of
2178          * all the queues that reference the
2179          * waker queue through their
2180          * waker_bfqq pointer. When the waker
2181          * queue exits, the waker_bfqq pointer
2182          * of all the queues in the woken_list
2183          * is reset.
2184          *
2185          * In addition, if bfqq is already in
2186          * the woken_list of a waker queue,
2187          * then, before being inserted into
2188          * the woken_list of a new waker
2189          * queue, bfqq must be removed from
2190          * the woken_list of the old waker
2191          * queue.
2192          */
2193         if (!hlist_unhashed(&bfqq->woken_list_node))
2194             hlist_del_init(&bfqq->woken_list_node);
2195         hlist_add_head(&bfqq->woken_list_node,
2196                    &bfqd->last_completed_rq_bfqq->woken_list);
2197     }
2198 }
2199 
2200 static void bfq_add_request(struct request *rq)
2201 {
2202     struct bfq_queue *bfqq = RQ_BFQQ(rq);
2203     struct bfq_data *bfqd = bfqq->bfqd;
2204     struct request *next_rq, *prev;
2205     unsigned int old_wr_coeff = bfqq->wr_coeff;
2206     bool interactive = false;
2207     u64 now_ns = ktime_get_ns();
2208 
2209     bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
2210     bfqq->queued[rq_is_sync(rq)]++;
2211     /*
2212      * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2213      * may be read without holding the lock in bfq_has_work().
2214      */
2215     WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
2216 
2217     if (bfq_bfqq_sync(bfqq) && RQ_BIC(rq)->requests <= 1) {
2218         bfq_check_waker(bfqd, bfqq, now_ns);
2219 
2220         /*
2221          * Periodically reset inject limit, to make sure that
2222          * the latter eventually drops in case workload
2223          * changes, see step (3) in the comments on
2224          * bfq_update_inject_limit().
2225          */
2226         if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2227                          msecs_to_jiffies(1000)))
2228             bfq_reset_inject_limit(bfqd, bfqq);
2229 
2230         /*
2231          * The following conditions must hold to setup a new
2232          * sampling of total service time, and then a new
2233          * update of the inject limit:
2234          * - bfqq is in service, because the total service
2235          *   time is evaluated only for the I/O requests of
2236          *   the queues in service;
2237          * - this is the right occasion to compute or to
2238          *   lower the baseline total service time, because
2239          *   there are actually no requests in the drive,
2240          *   or
2241          *   the baseline total service time is available, and
2242          *   this is the right occasion to compute the other
2243          *   quantity needed to update the inject limit, i.e.,
2244          *   the total service time caused by the amount of
2245          *   injection allowed by the current value of the
2246          *   limit. It is the right occasion because injection
2247          *   has actually been performed during the service
2248          *   hole, and there are still in-flight requests,
2249          *   which are very likely to be exactly the injected
2250          *   requests, or part of them;
2251          * - the minimum interval for sampling the total
2252          *   service time and updating the inject limit has
2253          *   elapsed.
2254          */
2255         if (bfqq == bfqd->in_service_queue &&
2256             (bfqd->rq_in_driver == 0 ||
2257              (bfqq->last_serv_time_ns > 0 &&
2258               bfqd->rqs_injected && bfqd->rq_in_driver > 0)) &&
2259             time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2260                           msecs_to_jiffies(10))) {
2261             bfqd->last_empty_occupied_ns = ktime_get_ns();
2262             /*
2263              * Start the state machine for measuring the
2264              * total service time of rq: setting
2265              * wait_dispatch will cause bfqd->waited_rq to
2266              * be set when rq will be dispatched.
2267              */
2268             bfqd->wait_dispatch = true;
2269             /*
2270              * If there is no I/O in service in the drive,
2271              * then possible injection occurred before the
2272              * arrival of rq will not affect the total
2273              * service time of rq. So the injection limit
2274              * must not be updated as a function of such
2275              * total service time, unless new injection
2276              * occurs before rq is completed. To have the
2277              * injection limit updated only in the latter
2278              * case, reset rqs_injected here (rqs_injected
2279              * will be set in case injection is performed
2280              * on bfqq before rq is completed).
2281              */
2282             if (bfqd->rq_in_driver == 0)
2283                 bfqd->rqs_injected = false;
2284         }
2285     }
2286 
2287     if (bfq_bfqq_sync(bfqq))
2288         bfq_update_io_intensity(bfqq, now_ns);
2289 
2290     elv_rb_add(&bfqq->sort_list, rq);
2291 
2292     /*
2293      * Check if this request is a better next-serve candidate.
2294      */
2295     prev = bfqq->next_rq;
2296     next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
2297     bfqq->next_rq = next_rq;
2298 
2299     /*
2300      * Adjust priority tree position, if next_rq changes.
2301      * See comments on bfq_pos_tree_add_move() for the unlikely().
2302      */
2303     if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2304         bfq_pos_tree_add_move(bfqd, bfqq);
2305 
2306     if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2307         bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2308                          rq, &interactive);
2309     else {
2310         if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2311             time_is_before_jiffies(
2312                 bfqq->last_wr_start_finish +
2313                 bfqd->bfq_wr_min_inter_arr_async)) {
2314             bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2315             bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2316 
2317             bfqd->wr_busy_queues++;
2318             bfqq->entity.prio_changed = 1;
2319         }
2320         if (prev != bfqq->next_rq)
2321             bfq_updated_next_req(bfqd, bfqq);
2322     }
2323 
2324     /*
2325      * Assign jiffies to last_wr_start_finish in the following
2326      * cases:
2327      *
2328      * . if bfqq is not going to be weight-raised, because, for
2329      *   non weight-raised queues, last_wr_start_finish stores the
2330      *   arrival time of the last request; as of now, this piece
2331      *   of information is used only for deciding whether to
2332      *   weight-raise async queues
2333      *
2334      * . if bfqq is not weight-raised, because, if bfqq is now
2335      *   switching to weight-raised, then last_wr_start_finish
2336      *   stores the time when weight-raising starts
2337      *
2338      * . if bfqq is interactive, because, regardless of whether
2339      *   bfqq is currently weight-raised, the weight-raising
2340      *   period must start or restart (this case is considered
2341      *   separately because it is not detected by the above
2342      *   conditions, if bfqq is already weight-raised)
2343      *
2344      * last_wr_start_finish has to be updated also if bfqq is soft
2345      * real-time, because the weight-raising period is constantly
2346      * restarted on idle-to-busy transitions for these queues, but
2347      * this is already done in bfq_bfqq_handle_idle_busy_switch if
2348      * needed.
2349      */
2350     if (bfqd->low_latency &&
2351         (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2352         bfqq->last_wr_start_finish = jiffies;
2353 }
2354 
2355 static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2356                       struct bio *bio,
2357                       struct request_queue *q)
2358 {
2359     struct bfq_queue *bfqq = bfqd->bio_bfqq;
2360 
2361 
2362     if (bfqq)
2363         return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2364 
2365     return NULL;
2366 }
2367 
2368 static sector_t get_sdist(sector_t last_pos, struct request *rq)
2369 {
2370     if (last_pos)
2371         return abs(blk_rq_pos(rq) - last_pos);
2372 
2373     return 0;
2374 }
2375 
2376 #if 0 /* Still not clear if we can do without next two functions */
2377 static void bfq_activate_request(struct request_queue *q, struct request *rq)
2378 {
2379     struct bfq_data *bfqd = q->elevator->elevator_data;
2380 
2381     bfqd->rq_in_driver++;
2382 }
2383 
2384 static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
2385 {
2386     struct bfq_data *bfqd = q->elevator->elevator_data;
2387 
2388     bfqd->rq_in_driver--;
2389 }
2390 #endif
2391 
2392 static void bfq_remove_request(struct request_queue *q,
2393                    struct request *rq)
2394 {
2395     struct bfq_queue *bfqq = RQ_BFQQ(rq);
2396     struct bfq_data *bfqd = bfqq->bfqd;
2397     const int sync = rq_is_sync(rq);
2398 
2399     if (bfqq->next_rq == rq) {
2400         bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
2401         bfq_updated_next_req(bfqd, bfqq);
2402     }
2403 
2404     if (rq->queuelist.prev != &rq->queuelist)
2405         list_del_init(&rq->queuelist);
2406     bfqq->queued[sync]--;
2407     /*
2408      * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2409      * may be read without holding the lock in bfq_has_work().
2410      */
2411     WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
2412     elv_rb_del(&bfqq->sort_list, rq);
2413 
2414     elv_rqhash_del(q, rq);
2415     if (q->last_merge == rq)
2416         q->last_merge = NULL;
2417 
2418     if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2419         bfqq->next_rq = NULL;
2420 
2421         if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2422             bfq_del_bfqq_busy(bfqd, bfqq, false);
2423             /*
2424              * bfqq emptied. In normal operation, when
2425              * bfqq is empty, bfqq->entity.service and
2426              * bfqq->entity.budget must contain,
2427              * respectively, the service received and the
2428              * budget used last time bfqq emptied. These
2429              * facts do not hold in this case, as at least
2430              * this last removal occurred while bfqq is
2431              * not in service. To avoid inconsistencies,
2432              * reset both bfqq->entity.service and
2433              * bfqq->entity.budget, if bfqq has still a
2434              * process that may issue I/O requests to it.
2435              */
2436             bfqq->entity.budget = bfqq->entity.service = 0;
2437         }
2438 
2439         /*
2440          * Remove queue from request-position tree as it is empty.
2441          */
2442         if (bfqq->pos_root) {
2443             rb_erase(&bfqq->pos_node, bfqq->pos_root);
2444             bfqq->pos_root = NULL;
2445         }
2446     } else {
2447         /* see comments on bfq_pos_tree_add_move() for the unlikely() */
2448         if (unlikely(!bfqd->nonrot_with_queueing))
2449             bfq_pos_tree_add_move(bfqd, bfqq);
2450     }
2451 
2452     if (rq->cmd_flags & REQ_META)
2453         bfqq->meta_pending--;
2454 
2455 }
2456 
2457 static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
2458         unsigned int nr_segs)
2459 {
2460     struct bfq_data *bfqd = q->elevator->elevator_data;
2461     struct request *free = NULL;
2462     /*
2463      * bfq_bic_lookup grabs the queue_lock: invoke it now and
2464      * store its return value for later use, to avoid nesting
2465      * queue_lock inside the bfqd->lock. We assume that the bic
2466      * returned by bfq_bic_lookup does not go away before
2467      * bfqd->lock is taken.
2468      */
2469     struct bfq_io_cq *bic = bfq_bic_lookup(q);
2470     bool ret;
2471 
2472     spin_lock_irq(&bfqd->lock);
2473 
2474     if (bic) {
2475         /*
2476          * Make sure cgroup info is uptodate for current process before
2477          * considering the merge.
2478          */
2479         bfq_bic_update_cgroup(bic, bio);
2480 
2481         bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
2482     } else {
2483         bfqd->bio_bfqq = NULL;
2484     }
2485     bfqd->bio_bic = bic;
2486 
2487     ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
2488 
2489     spin_unlock_irq(&bfqd->lock);
2490     if (free)
2491         blk_mq_free_request(free);
2492 
2493     return ret;
2494 }
2495 
2496 static int bfq_request_merge(struct request_queue *q, struct request **req,
2497                  struct bio *bio)
2498 {
2499     struct bfq_data *bfqd = q->elevator->elevator_data;
2500     struct request *__rq;
2501 
2502     __rq = bfq_find_rq_fmerge(bfqd, bio, q);
2503     if (__rq && elv_bio_merge_ok(__rq, bio)) {
2504         *req = __rq;
2505 
2506         if (blk_discard_mergable(__rq))
2507             return ELEVATOR_DISCARD_MERGE;
2508         return ELEVATOR_FRONT_MERGE;
2509     }
2510 
2511     return ELEVATOR_NO_MERGE;
2512 }
2513 
2514 static void bfq_request_merged(struct request_queue *q, struct request *req,
2515                    enum elv_merge type)
2516 {
2517     if (type == ELEVATOR_FRONT_MERGE &&
2518         rb_prev(&req->rb_node) &&
2519         blk_rq_pos(req) <
2520         blk_rq_pos(container_of(rb_prev(&req->rb_node),
2521                     struct request, rb_node))) {
2522         struct bfq_queue *bfqq = RQ_BFQQ(req);
2523         struct bfq_data *bfqd;
2524         struct request *prev, *next_rq;
2525 
2526         if (!bfqq)
2527             return;
2528 
2529         bfqd = bfqq->bfqd;
2530 
2531         /* Reposition request in its sort_list */
2532         elv_rb_del(&bfqq->sort_list, req);
2533         elv_rb_add(&bfqq->sort_list, req);
2534 
2535         /* Choose next request to be served for bfqq */
2536         prev = bfqq->next_rq;
2537         next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
2538                      bfqd->last_position);
2539         bfqq->next_rq = next_rq;
2540         /*
2541          * If next_rq changes, update both the queue's budget to
2542          * fit the new request and the queue's position in its
2543          * rq_pos_tree.
2544          */
2545         if (prev != bfqq->next_rq) {
2546             bfq_updated_next_req(bfqd, bfqq);
2547             /*
2548              * See comments on bfq_pos_tree_add_move() for
2549              * the unlikely().
2550              */
2551             if (unlikely(!bfqd->nonrot_with_queueing))
2552                 bfq_pos_tree_add_move(bfqd, bfqq);
2553         }
2554     }
2555 }
2556 
2557 /*
2558  * This function is called to notify the scheduler that the requests
2559  * rq and 'next' have been merged, with 'next' going away.  BFQ
2560  * exploits this hook to address the following issue: if 'next' has a
2561  * fifo_time lower that rq, then the fifo_time of rq must be set to
2562  * the value of 'next', to not forget the greater age of 'next'.
2563  *
2564  * NOTE: in this function we assume that rq is in a bfq_queue, basing
2565  * on that rq is picked from the hash table q->elevator->hash, which,
2566  * in its turn, is filled only with I/O requests present in
2567  * bfq_queues, while BFQ is in use for the request queue q. In fact,
2568  * the function that fills this hash table (elv_rqhash_add) is called
2569  * only by bfq_insert_request.
2570  */
2571 static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2572                 struct request *next)
2573 {
2574     struct bfq_queue *bfqq = RQ_BFQQ(rq),
2575         *next_bfqq = RQ_BFQQ(next);
2576 
2577     if (!bfqq)
2578         goto remove;
2579 
2580     /*
2581      * If next and rq belong to the same bfq_queue and next is older
2582      * than rq, then reposition rq in the fifo (by substituting next
2583      * with rq). Otherwise, if next and rq belong to different
2584      * bfq_queues, never reposition rq: in fact, we would have to
2585      * reposition it with respect to next's position in its own fifo,
2586      * which would most certainly be too expensive with respect to
2587      * the benefits.
2588      */
2589     if (bfqq == next_bfqq &&
2590         !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
2591         next->fifo_time < rq->fifo_time) {
2592         list_del_init(&rq->queuelist);
2593         list_replace_init(&next->queuelist, &rq->queuelist);
2594         rq->fifo_time = next->fifo_time;
2595     }
2596 
2597     if (bfqq->next_rq == next)
2598         bfqq->next_rq = rq;
2599 
2600     bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
2601 remove:
2602     /* Merged request may be in the IO scheduler. Remove it. */
2603     if (!RB_EMPTY_NODE(&next->rb_node)) {
2604         bfq_remove_request(next->q, next);
2605         if (next_bfqq)
2606             bfqg_stats_update_io_remove(bfqq_group(next_bfqq),
2607                             next->cmd_flags);
2608     }
2609 }
2610 
2611 /* Must be called with bfqq != NULL */
2612 static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2613 {
2614     /*
2615      * If bfqq has been enjoying interactive weight-raising, then
2616      * reset soft_rt_next_start. We do it for the following
2617      * reason. bfqq may have been conveying the I/O needed to load
2618      * a soft real-time application. Such an application actually
2619      * exhibits a soft real-time I/O pattern after it finishes
2620      * loading, and finally starts doing its job. But, if bfqq has
2621      * been receiving a lot of bandwidth so far (likely to happen
2622      * on a fast device), then soft_rt_next_start now contains a
2623      * high value that. So, without this reset, bfqq would be
2624      * prevented from being possibly considered as soft_rt for a
2625      * very long time.
2626      */
2627 
2628     if (bfqq->wr_cur_max_time !=
2629         bfqq->bfqd->bfq_wr_rt_max_time)
2630         bfqq->soft_rt_next_start = jiffies;
2631 
2632     if (bfq_bfqq_busy(bfqq))
2633         bfqq->bfqd->wr_busy_queues--;
2634     bfqq->wr_coeff = 1;
2635     bfqq->wr_cur_max_time = 0;
2636     bfqq->last_wr_start_finish = jiffies;
2637     /*
2638      * Trigger a weight change on the next invocation of
2639      * __bfq_entity_update_weight_prio.
2640      */
2641     bfqq->entity.prio_changed = 1;
2642 }
2643 
2644 void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2645                  struct bfq_group *bfqg)
2646 {
2647     int i, j;
2648 
2649     for (i = 0; i < 2; i++)
2650         for (j = 0; j < IOPRIO_NR_LEVELS; j++)
2651             if (bfqg->async_bfqq[i][j])
2652                 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
2653     if (bfqg->async_idle_bfqq)
2654         bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
2655 }
2656 
2657 static void bfq_end_wr(struct bfq_data *bfqd)
2658 {
2659     struct bfq_queue *bfqq;
2660 
2661     spin_lock_irq(&bfqd->lock);
2662 
2663     list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
2664         bfq_bfqq_end_wr(bfqq);
2665     list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2666         bfq_bfqq_end_wr(bfqq);
2667     bfq_end_wr_async(bfqd);
2668 
2669     spin_unlock_irq(&bfqd->lock);
2670 }
2671 
2672 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2673 {
2674     if (request)
2675         return blk_rq_pos(io_struct);
2676     else
2677         return ((struct bio *)io_struct)->bi_iter.bi_sector;
2678 }
2679 
2680 static int bfq_rq_close_to_sector(void *io_struct, bool request,
2681                   sector_t sector)
2682 {
2683     return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2684            BFQQ_CLOSE_THR;
2685 }
2686 
2687 static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2688                      struct bfq_queue *bfqq,
2689                      sector_t sector)
2690 {
2691     struct rb_root *root = &bfqq_group(bfqq)->rq_pos_tree;
2692     struct rb_node *parent, *node;
2693     struct bfq_queue *__bfqq;
2694 
2695     if (RB_EMPTY_ROOT(root))
2696         return NULL;
2697 
2698     /*
2699      * First, if we find a request starting at the end of the last
2700      * request, choose it.
2701      */
2702     __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2703     if (__bfqq)
2704         return __bfqq;
2705 
2706     /*
2707      * If the exact sector wasn't found, the parent of the NULL leaf
2708      * will contain the closest sector (rq_pos_tree sorted by
2709      * next_request position).
2710      */
2711     __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2712     if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2713         return __bfqq;
2714 
2715     if (blk_rq_pos(__bfqq->next_rq) < sector)
2716         node = rb_next(&__bfqq->pos_node);
2717     else
2718         node = rb_prev(&__bfqq->pos_node);
2719     if (!node)
2720         return NULL;
2721 
2722     __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2723     if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2724         return __bfqq;
2725 
2726     return NULL;
2727 }
2728 
2729 static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2730                            struct bfq_queue *cur_bfqq,
2731                            sector_t sector)
2732 {
2733     struct bfq_queue *bfqq;
2734 
2735     /*
2736      * We shall notice if some of the queues are cooperating,
2737      * e.g., working closely on the same area of the device. In
2738      * that case, we can group them together and: 1) don't waste
2739      * time idling, and 2) serve the union of their requests in
2740      * the best possible order for throughput.
2741      */
2742     bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2743     if (!bfqq || bfqq == cur_bfqq)
2744         return NULL;
2745 
2746     return bfqq;
2747 }
2748 
2749 static struct bfq_queue *
2750 bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2751 {
2752     int process_refs, new_process_refs;
2753     struct bfq_queue *__bfqq;
2754 
2755     /*
2756      * If there are no process references on the new_bfqq, then it is
2757      * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2758      * may have dropped their last reference (not just their last process
2759      * reference).
2760      */
2761     if (!bfqq_process_refs(new_bfqq))
2762         return NULL;
2763 
2764     /* Avoid a circular list and skip interim queue merges. */
2765     while ((__bfqq = new_bfqq->new_bfqq)) {
2766         if (__bfqq == bfqq)
2767             return NULL;
2768         new_bfqq = __bfqq;
2769     }
2770 
2771     process_refs = bfqq_process_refs(bfqq);
2772     new_process_refs = bfqq_process_refs(new_bfqq);
2773     /*
2774      * If the process for the bfqq has gone away, there is no
2775      * sense in merging the queues.
2776      */
2777     if (process_refs == 0 || new_process_refs == 0)
2778         return NULL;
2779 
2780     /*
2781      * Make sure merged queues belong to the same parent. Parents could
2782      * have changed since the time we decided the two queues are suitable
2783      * for merging.
2784      */
2785     if (new_bfqq->entity.parent != bfqq->entity.parent)
2786         return NULL;
2787 
2788     bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2789         new_bfqq->pid);
2790 
2791     /*
2792      * Merging is just a redirection: the requests of the process
2793      * owning one of the two queues are redirected to the other queue.
2794      * The latter queue, in its turn, is set as shared if this is the
2795      * first time that the requests of some process are redirected to
2796      * it.
2797      *
2798      * We redirect bfqq to new_bfqq and not the opposite, because
2799      * we are in the context of the process owning bfqq, thus we
2800      * have the io_cq of this process. So we can immediately
2801      * configure this io_cq to redirect the requests of the
2802      * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2803      * not available any more (new_bfqq->bic == NULL).
2804      *
2805      * Anyway, even in case new_bfqq coincides with the in-service
2806      * queue, redirecting requests the in-service queue is the
2807      * best option, as we feed the in-service queue with new
2808      * requests close to the last request served and, by doing so,
2809      * are likely to increase the throughput.
2810      */
2811     bfqq->new_bfqq = new_bfqq;
2812     /*
2813      * The above assignment schedules the following redirections:
2814      * each time some I/O for bfqq arrives, the process that
2815      * generated that I/O is disassociated from bfqq and
2816      * associated with new_bfqq. Here we increases new_bfqq->ref
2817      * in advance, adding the number of processes that are
2818      * expected to be associated with new_bfqq as they happen to
2819      * issue I/O.
2820      */
2821     new_bfqq->ref += process_refs;
2822     return new_bfqq;
2823 }
2824 
2825 static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2826                     struct bfq_queue *new_bfqq)
2827 {
2828     if (bfq_too_late_for_merging(new_bfqq))
2829         return false;
2830 
2831     if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2832         (bfqq->ioprio_class != new_bfqq->ioprio_class))
2833         return false;
2834 
2835     /*
2836      * If either of the queues has already been detected as seeky,
2837      * then merging it with the other queue is unlikely to lead to
2838      * sequential I/O.
2839      */
2840     if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2841         return false;
2842 
2843     /*
2844      * Interleaved I/O is known to be done by (some) applications
2845      * only for reads, so it does not make sense to merge async
2846      * queues.
2847      */
2848     if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2849         return false;
2850 
2851     return true;
2852 }
2853 
2854 static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
2855                          struct bfq_queue *bfqq);
2856 
2857 /*
2858  * Attempt to schedule a merge of bfqq with the currently in-service
2859  * queue or with a close queue among the scheduled queues.  Return
2860  * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2861  * structure otherwise.
2862  *
2863  * The OOM queue is not allowed to participate to cooperation: in fact, since
2864  * the requests temporarily redirected to the OOM queue could be redirected
2865  * again to dedicated queues at any time, the state needed to correctly
2866  * handle merging with the OOM queue would be quite complex and expensive
2867  * to maintain. Besides, in such a critical condition as an out of memory,
2868  * the benefits of queue merging may be little relevant, or even negligible.
2869  *
2870  * WARNING: queue merging may impair fairness among non-weight raised
2871  * queues, for at least two reasons: 1) the original weight of a
2872  * merged queue may change during the merged state, 2) even being the
2873  * weight the same, a merged queue may be bloated with many more
2874  * requests than the ones produced by its originally-associated
2875  * process.
2876  */
2877 static struct bfq_queue *
2878 bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2879              void *io_struct, bool request, struct bfq_io_cq *bic)
2880 {
2881     struct bfq_queue *in_service_bfqq, *new_bfqq;
2882 
2883     /* if a merge has already been setup, then proceed with that first */
2884     if (bfqq->new_bfqq)
2885         return bfqq->new_bfqq;
2886 
2887     /*
2888      * Check delayed stable merge for rotational or non-queueing
2889      * devs. For this branch to be executed, bfqq must not be
2890      * currently merged with some other queue (i.e., bfqq->bic
2891      * must be non null). If we considered also merged queues,
2892      * then we should also check whether bfqq has already been
2893      * merged with bic->stable_merge_bfqq. But this would be
2894      * costly and complicated.
2895      */
2896     if (unlikely(!bfqd->nonrot_with_queueing)) {
2897         /*
2898          * Make sure also that bfqq is sync, because
2899          * bic->stable_merge_bfqq may point to some queue (for
2900          * stable merging) also if bic is associated with a
2901          * sync queue, but this bfqq is async
2902          */
2903         if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq &&
2904             !bfq_bfqq_just_created(bfqq) &&
2905             time_is_before_jiffies(bfqq->split_time +
2906                       msecs_to_jiffies(bfq_late_stable_merging)) &&
2907             time_is_before_jiffies(bfqq->creation_time +
2908                        msecs_to_jiffies(bfq_late_stable_merging))) {
2909             struct bfq_queue *stable_merge_bfqq =
2910                 bic->stable_merge_bfqq;
2911             int proc_ref = min(bfqq_process_refs(bfqq),
2912                        bfqq_process_refs(stable_merge_bfqq));
2913 
2914             /* deschedule stable merge, because done or aborted here */
2915             bfq_put_stable_ref(stable_merge_bfqq);
2916 
2917             bic->stable_merge_bfqq = NULL;
2918 
2919             if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
2920                 proc_ref > 0) {
2921                 /* next function will take at least one ref */
2922                 struct bfq_queue *new_bfqq =
2923                     bfq_setup_merge(bfqq, stable_merge_bfqq);
2924 
2925                 if (new_bfqq) {
2926                     bic->stably_merged = true;
2927                     if (new_bfqq->bic)
2928                         new_bfqq->bic->stably_merged =
2929                                     true;
2930                 }
2931                 return new_bfqq;
2932             } else
2933                 return NULL;
2934         }
2935     }
2936 
2937     /*
2938      * Do not perform queue merging if the device is non
2939      * rotational and performs internal queueing. In fact, such a
2940      * device reaches a high speed through internal parallelism
2941      * and pipelining. This means that, to reach a high
2942      * throughput, it must have many requests enqueued at the same
2943      * time. But, in this configuration, the internal scheduling
2944      * algorithm of the device does exactly the job of queue
2945      * merging: it reorders requests so as to obtain as much as
2946      * possible a sequential I/O pattern. As a consequence, with
2947      * the workload generated by processes doing interleaved I/O,
2948      * the throughput reached by the device is likely to be the
2949      * same, with and without queue merging.
2950      *
2951      * Disabling merging also provides a remarkable benefit in
2952      * terms of throughput. Merging tends to make many workloads
2953      * artificially more uneven, because of shared queues
2954      * remaining non empty for incomparably more time than
2955      * non-merged queues. This may accentuate workload
2956      * asymmetries. For example, if one of the queues in a set of
2957      * merged queues has a higher weight than a normal queue, then
2958      * the shared queue may inherit such a high weight and, by
2959      * staying almost always active, may force BFQ to perform I/O
2960      * plugging most of the time. This evidently makes it harder
2961      * for BFQ to let the device reach a high throughput.
2962      *
2963      * Finally, the likely() macro below is not used because one
2964      * of the two branches is more likely than the other, but to
2965      * have the code path after the following if() executed as
2966      * fast as possible for the case of a non rotational device
2967      * with queueing. We want it because this is the fastest kind
2968      * of device. On the opposite end, the likely() may lengthen
2969      * the execution time of BFQ for the case of slower devices
2970      * (rotational or at least without queueing). But in this case
2971      * the execution time of BFQ matters very little, if not at
2972      * all.
2973      */
2974     if (likely(bfqd->nonrot_with_queueing))
2975         return NULL;
2976 
2977     /*
2978      * Prevent bfqq from being merged if it has been created too
2979      * long ago. The idea is that true cooperating processes, and
2980      * thus their associated bfq_queues, are supposed to be
2981      * created shortly after each other. This is the case, e.g.,
2982      * for KVM/QEMU and dump I/O threads. Basing on this
2983      * assumption, the following filtering greatly reduces the
2984      * probability that two non-cooperating processes, which just
2985      * happen to do close I/O for some short time interval, have
2986      * their queues merged by mistake.
2987      */
2988     if (bfq_too_late_for_merging(bfqq))
2989         return NULL;
2990 
2991     if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
2992         return NULL;
2993 
2994     /* If there is only one backlogged queue, don't search. */
2995     if (bfq_tot_busy_queues(bfqd) == 1)
2996         return NULL;
2997 
2998     in_service_bfqq = bfqd->in_service_queue;
2999 
3000     if (in_service_bfqq && in_service_bfqq != bfqq &&
3001         likely(in_service_bfqq != &bfqd->oom_bfqq) &&
3002         bfq_rq_close_to_sector(io_struct, request,
3003                    bfqd->in_serv_last_pos) &&
3004         bfqq->entity.parent == in_service_bfqq->entity.parent &&
3005         bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
3006         new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
3007         if (new_bfqq)
3008             return new_bfqq;
3009     }
3010     /*
3011      * Check whether there is a cooperator among currently scheduled
3012      * queues. The only thing we need is that the bio/request is not
3013      * NULL, as we need it to establish whether a cooperator exists.
3014      */
3015     new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
3016             bfq_io_struct_pos(io_struct, request));
3017 
3018     if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
3019         bfq_may_be_close_cooperator(bfqq, new_bfqq))
3020         return bfq_setup_merge(bfqq, new_bfqq);
3021 
3022     return NULL;
3023 }
3024 
3025 static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
3026 {
3027     struct bfq_io_cq *bic = bfqq->bic;
3028 
3029     /*
3030      * If !bfqq->bic, the queue is already shared or its requests
3031      * have already been redirected to a shared queue; both idle window
3032      * and weight raising state have already been saved. Do nothing.
3033      */
3034     if (!bic)
3035         return;
3036 
3037     bic->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
3038     bic->saved_inject_limit = bfqq->inject_limit;
3039     bic->saved_decrease_time_jif = bfqq->decrease_time_jif;
3040 
3041     bic->saved_weight = bfqq->entity.orig_weight;
3042     bic->saved_ttime = bfqq->ttime;
3043     bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
3044     bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
3045     bic->saved_io_start_time = bfqq->io_start_time;
3046     bic->saved_tot_idle_time = bfqq->tot_idle_time;
3047     bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
3048     bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
3049     if (unlikely(bfq_bfqq_just_created(bfqq) &&
3050              !bfq_bfqq_in_large_burst(bfqq) &&
3051              bfqq->bfqd->low_latency)) {
3052         /*
3053          * bfqq being merged right after being created: bfqq
3054          * would have deserved interactive weight raising, but
3055          * did not make it to be set in a weight-raised state,
3056          * because of this early merge. Store directly the
3057          * weight-raising state that would have been assigned
3058          * to bfqq, so that to avoid that bfqq unjustly fails
3059          * to enjoy weight raising if split soon.
3060          */
3061         bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
3062         bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
3063         bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
3064         bic->saved_last_wr_start_finish = jiffies;
3065     } else {
3066         bic->saved_wr_coeff = bfqq->wr_coeff;
3067         bic->saved_wr_start_at_switch_to_srt =
3068             bfqq->wr_start_at_switch_to_srt;
3069         bic->saved_service_from_wr = bfqq->service_from_wr;
3070         bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
3071         bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
3072     }
3073 }
3074 
3075 
3076 static void
3077 bfq_reassign_last_bfqq(struct bfq_queue *cur_bfqq, struct bfq_queue *new_bfqq)
3078 {
3079     if (cur_bfqq->entity.parent &&
3080         cur_bfqq->entity.parent->last_bfqq_created == cur_bfqq)
3081         cur_bfqq->entity.parent->last_bfqq_created = new_bfqq;
3082     else if (cur_bfqq->bfqd && cur_bfqq->bfqd->last_bfqq_created == cur_bfqq)
3083         cur_bfqq->bfqd->last_bfqq_created = new_bfqq;
3084 }
3085 
3086 void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3087 {
3088     /*
3089      * To prevent bfqq's service guarantees from being violated,
3090      * bfqq may be left busy, i.e., queued for service, even if
3091      * empty (see comments in __bfq_bfqq_expire() for
3092      * details). But, if no process will send requests to bfqq any
3093      * longer, then there is no point in keeping bfqq queued for
3094      * service. In addition, keeping bfqq queued for service, but
3095      * with no process ref any longer, may have caused bfqq to be
3096      * freed when dequeued from service. But this is assumed to
3097      * never happen.
3098      */
3099     if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
3100         bfqq != bfqd->in_service_queue)
3101         bfq_del_bfqq_busy(bfqd, bfqq, false);
3102 
3103     bfq_reassign_last_bfqq(bfqq, NULL);
3104 
3105     bfq_put_queue(bfqq);
3106 }
3107 
3108 static void
3109 bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
3110         struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
3111 {
3112     bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
3113         (unsigned long)new_bfqq->pid);
3114     /* Save weight raising and idle window of the merged queues */
3115     bfq_bfqq_save_state(bfqq);
3116     bfq_bfqq_save_state(new_bfqq);
3117     if (bfq_bfqq_IO_bound(bfqq))
3118         bfq_mark_bfqq_IO_bound(new_bfqq);
3119     bfq_clear_bfqq_IO_bound(bfqq);
3120 
3121     /*
3122      * The processes associated with bfqq are cooperators of the
3123      * processes associated with new_bfqq. So, if bfqq has a
3124      * waker, then assume that all these processes will be happy
3125      * to let bfqq's waker freely inject I/O when they have no
3126      * I/O.
3127      */
3128     if (bfqq->waker_bfqq && !new_bfqq->waker_bfqq &&
3129         bfqq->waker_bfqq != new_bfqq) {
3130         new_bfqq->waker_bfqq = bfqq->waker_bfqq;
3131         new_bfqq->tentative_waker_bfqq = NULL;
3132 
3133         /*
3134          * If the waker queue disappears, then
3135          * new_bfqq->waker_bfqq must be reset. So insert
3136          * new_bfqq into the woken_list of the waker. See
3137          * bfq_check_waker for details.
3138          */
3139         hlist_add_head(&new_bfqq->woken_list_node,
3140                    &new_bfqq->waker_bfqq->woken_list);
3141 
3142     }
3143 
3144     /*
3145      * If bfqq is weight-raised, then let new_bfqq inherit
3146      * weight-raising. To reduce false positives, neglect the case
3147      * where bfqq has just been created, but has not yet made it
3148      * to be weight-raised (which may happen because EQM may merge
3149      * bfqq even before bfq_add_request is executed for the first
3150      * time for bfqq). Handling this case would however be very
3151      * easy, thanks to the flag just_created.
3152      */
3153     if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
3154         new_bfqq->wr_coeff = bfqq->wr_coeff;
3155         new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
3156         new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
3157         new_bfqq->wr_start_at_switch_to_srt =
3158             bfqq->wr_start_at_switch_to_srt;
3159         if (bfq_bfqq_busy(new_bfqq))
3160             bfqd->wr_busy_queues++;
3161         new_bfqq->entity.prio_changed = 1;
3162     }
3163 
3164     if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
3165         bfqq->wr_coeff = 1;
3166         bfqq->entity.prio_changed = 1;
3167         if (bfq_bfqq_busy(bfqq))
3168             bfqd->wr_busy_queues--;
3169     }
3170 
3171     bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
3172              bfqd->wr_busy_queues);
3173 
3174     /*
3175      * Merge queues (that is, let bic redirect its requests to new_bfqq)
3176      */
3177     bic_set_bfqq(bic, new_bfqq, 1);
3178     bfq_mark_bfqq_coop(new_bfqq);
3179     /*
3180      * new_bfqq now belongs to at least two bics (it is a shared queue):
3181      * set new_bfqq->bic to NULL. bfqq either:
3182      * - does not belong to any bic any more, and hence bfqq->bic must
3183      *   be set to NULL, or
3184      * - is a queue whose owning bics have already been redirected to a
3185      *   different queue, hence the queue is destined to not belong to
3186      *   any bic soon and bfqq->bic is already NULL (therefore the next
3187      *   assignment causes no harm).
3188      */
3189     new_bfqq->bic = NULL;
3190     /*
3191      * If the queue is shared, the pid is the pid of one of the associated
3192      * processes. Which pid depends on the exact sequence of merge events
3193      * the queue underwent. So printing such a pid is useless and confusing
3194      * because it reports a random pid between those of the associated
3195      * processes.
3196      * We mark such a queue with a pid -1, and then print SHARED instead of
3197      * a pid in logging messages.
3198      */
3199     new_bfqq->pid = -1;
3200     bfqq->bic = NULL;
3201 
3202     bfq_reassign_last_bfqq(bfqq, new_bfqq);
3203 
3204     bfq_release_process_ref(bfqd, bfqq);
3205 }
3206 
3207 static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
3208                 struct bio *bio)
3209 {
3210     struct bfq_data *bfqd = q->elevator->elevator_data;
3211     bool is_sync = op_is_sync(bio->bi_opf);
3212     struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
3213 
3214     /*
3215      * Disallow merge of a sync bio into an async request.
3216      */
3217     if (is_sync && !rq_is_sync(rq))
3218         return false;
3219 
3220     /*
3221      * Lookup the bfqq that this bio will be queued with. Allow
3222      * merge only if rq is queued there.
3223      */
3224     if (!bfqq)
3225         return false;
3226 
3227     /*
3228      * We take advantage of this function to perform an early merge
3229      * of the queues of possible cooperating processes.
3230      */
3231     new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false, bfqd->bio_bic);
3232     if (new_bfqq) {
3233         /*
3234          * bic still points to bfqq, then it has not yet been
3235          * redirected to some other bfq_queue, and a queue
3236          * merge between bfqq and new_bfqq can be safely
3237          * fulfilled, i.e., bic can be redirected to new_bfqq
3238          * and bfqq can be put.
3239          */
3240         bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
3241                 new_bfqq);
3242         /*
3243          * If we get here, bio will be queued into new_queue,
3244          * so use new_bfqq to decide whether bio and rq can be
3245          * merged.
3246          */
3247         bfqq = new_bfqq;
3248 
3249         /*
3250          * Change also bqfd->bio_bfqq, as
3251          * bfqd->bio_bic now points to new_bfqq, and
3252          * this function may be invoked again (and then may
3253          * use again bqfd->bio_bfqq).
3254          */
3255         bfqd->bio_bfqq = bfqq;
3256     }
3257 
3258     return bfqq == RQ_BFQQ(rq);
3259 }
3260 
3261 /*
3262  * Set the maximum time for the in-service queue to consume its
3263  * budget. This prevents seeky processes from lowering the throughput.
3264  * In practice, a time-slice service scheme is used with seeky
3265  * processes.
3266  */
3267 static void bfq_set_budget_timeout(struct bfq_data *bfqd,
3268                    struct bfq_queue *bfqq)
3269 {
3270     unsigned int timeout_coeff;
3271 
3272     if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
3273         timeout_coeff = 1;
3274     else
3275         timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
3276 
3277     bfqd->last_budget_start = ktime_get();
3278 
3279     bfqq->budget_timeout = jiffies +
3280         bfqd->bfq_timeout * timeout_coeff;
3281 }
3282 
3283 static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
3284                        struct bfq_queue *bfqq)
3285 {
3286     if (bfqq) {
3287         bfq_clear_bfqq_fifo_expire(bfqq);
3288 
3289         bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
3290 
3291         if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
3292             bfqq->wr_coeff > 1 &&
3293             bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
3294             time_is_before_jiffies(bfqq->budget_timeout)) {
3295             /*
3296              * For soft real-time queues, move the start
3297              * of the weight-raising period forward by the
3298              * time the queue has not received any
3299              * service. Otherwise, a relatively long
3300              * service delay is likely to cause the
3301              * weight-raising period of the queue to end,
3302              * because of the short duration of the
3303              * weight-raising period of a soft real-time
3304              * queue.  It is worth noting that this move
3305              * is not so dangerous for the other queues,
3306              * because soft real-time queues are not
3307              * greedy.
3308              *
3309              * To not add a further variable, we use the
3310              * overloaded field budget_timeout to
3311              * determine for how long the queue has not
3312              * received service, i.e., how much time has
3313              * elapsed since the queue expired. However,
3314              * this is a little imprecise, because
3315              * budget_timeout is set to jiffies if bfqq
3316              * not only expires, but also remains with no
3317              * request.
3318              */
3319             if (time_after(bfqq->budget_timeout,
3320                        bfqq->last_wr_start_finish))
3321                 bfqq->last_wr_start_finish +=
3322                     jiffies - bfqq->budget_timeout;
3323             else
3324                 bfqq->last_wr_start_finish = jiffies;
3325         }
3326 
3327         bfq_set_budget_timeout(bfqd, bfqq);
3328         bfq_log_bfqq(bfqd, bfqq,
3329                  "set_in_service_queue, cur-budget = %d",
3330                  bfqq->entity.budget);
3331     }
3332 
3333     bfqd->in_service_queue = bfqq;
3334     bfqd->in_serv_last_pos = 0;
3335 }
3336 
3337 /*
3338  * Get and set a new queue for service.
3339  */
3340 static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
3341 {
3342     struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
3343 
3344     __bfq_set_in_service_queue(bfqd, bfqq);
3345     return bfqq;
3346 }
3347 
3348 static void bfq_arm_slice_timer(struct bfq_data *bfqd)
3349 {
3350     struct bfq_queue *bfqq = bfqd->in_service_queue;
3351     u32 sl;
3352 
3353     bfq_mark_bfqq_wait_request(bfqq);
3354 
3355     /*
3356      * We don't want to idle for seeks, but we do want to allow
3357      * fair distribution of slice time for a process doing back-to-back
3358      * seeks. So allow a little bit of time for him to submit a new rq.
3359      */
3360     sl = bfqd->bfq_slice_idle;
3361     /*
3362      * Unless the queue is being weight-raised or the scenario is
3363      * asymmetric, grant only minimum idle time if the queue
3364      * is seeky. A long idling is preserved for a weight-raised
3365      * queue, or, more in general, in an asymmetric scenario,
3366      * because a long idling is needed for guaranteeing to a queue
3367      * its reserved share of the throughput (in particular, it is
3368      * needed if the queue has a higher weight than some other
3369      * queue).
3370      */
3371     if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
3372         !bfq_asymmetric_scenario(bfqd, bfqq))
3373         sl = min_t(u64, sl, BFQ_MIN_TT);
3374     else if (bfqq->wr_coeff > 1)
3375         sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
3376 
3377     bfqd->last_idling_start = ktime_get();
3378     bfqd->last_idling_start_jiffies = jiffies;
3379 
3380     hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
3381               HRTIMER_MODE_REL);
3382     bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
3383 }
3384 
3385 /*
3386  * In autotuning mode, max_budget is dynamically recomputed as the
3387  * amount of sectors transferred in timeout at the estimated peak
3388  * rate. This enables BFQ to utilize a full timeslice with a full
3389  * budget, even if the in-service queue is served at peak rate. And
3390  * this maximises throughput with sequential workloads.
3391  */
3392 static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
3393 {
3394     return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3395         jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3396 }
3397 
3398 /*
3399  * Update parameters related to throughput and responsiveness, as a
3400  * function of the estimated peak rate. See comments on
3401  * bfq_calc_max_budget(), and on the ref_wr_duration array.
3402  */
3403 static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3404 {
3405     if (bfqd->bfq_user_max_budget == 0) {
3406         bfqd->bfq_max_budget =
3407             bfq_calc_max_budget(bfqd);
3408         bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3409     }
3410 }
3411 
3412 static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3413                        struct request *rq)
3414 {
3415     if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3416         bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
3417         bfqd->peak_rate_samples = 1;
3418         bfqd->sequential_samples = 0;
3419         bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3420             blk_rq_sectors(rq);
3421     } else /* no new rq dispatched, just reset the number of samples */
3422         bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3423 
3424     bfq_log(bfqd,
3425         "reset_rate_computation at end, sample %u/%u tot_sects %llu",
3426         bfqd->peak_rate_samples, bfqd->sequential_samples,
3427         bfqd->tot_sectors_dispatched);
3428 }
3429 
3430 static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3431 {
3432     u32 rate, weight, divisor;
3433 
3434     /*
3435      * For the convergence property to hold (see comments on
3436      * bfq_update_peak_rate()) and for the assessment to be
3437      * reliable, a minimum number of samples must be present, and
3438      * a minimum amount of time must have elapsed. If not so, do
3439      * not compute new rate. Just reset parameters, to get ready
3440      * for a new evaluation attempt.
3441      */
3442     if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3443         bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3444         goto reset_computation;
3445 
3446     /*
3447      * If a new request completion has occurred after last
3448      * dispatch, then, to approximate the rate at which requests
3449      * have been served by the device, it is more precise to
3450      * extend the observation interval to the last completion.
3451      */
3452     bfqd->delta_from_first =
3453         max_t(u64, bfqd->delta_from_first,
3454               bfqd->last_completion - bfqd->first_dispatch);
3455 
3456     /*
3457      * Rate computed in sects/usec, and not sects/nsec, for
3458      * precision issues.
3459      */
3460     rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3461             div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3462 
3463     /*
3464      * Peak rate not updated if:
3465      * - the percentage of sequential dispatches is below 3/4 of the
3466      *   total, and rate is below the current estimated peak rate
3467      * - rate is unreasonably high (> 20M sectors/sec)
3468      */
3469     if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3470          rate <= bfqd->peak_rate) ||
3471         rate > 20<<BFQ_RATE_SHIFT)
3472         goto reset_computation;
3473 
3474     /*
3475      * We have to update the peak rate, at last! To this purpose,
3476      * we use a low-pass filter. We compute the smoothing constant
3477      * of the filter as a function of the 'weight' of the new
3478      * measured rate.
3479      *
3480      * As can be seen in next formulas, we define this weight as a
3481      * quantity proportional to how sequential the workload is,
3482      * and to how long the observation time interval is.
3483      *
3484      * The weight runs from 0 to 8. The maximum value of the
3485      * weight, 8, yields the minimum value for the smoothing
3486      * constant. At this minimum value for the smoothing constant,
3487      * the measured rate contributes for half of the next value of
3488      * the estimated peak rate.
3489      *
3490      * So, the first step is to compute the weight as a function
3491      * of how sequential the workload is. Note that the weight
3492      * cannot reach 9, because bfqd->sequential_samples cannot
3493      * become equal to bfqd->peak_rate_samples, which, in its
3494      * turn, holds true because bfqd->sequential_samples is not
3495      * incremented for the first sample.
3496      */
3497     weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3498 
3499     /*
3500      * Second step: further refine the weight as a function of the
3501      * duration of the observation interval.
3502      */
3503     weight = min_t(u32, 8,
3504                div_u64(weight * bfqd->delta_from_first,
3505                    BFQ_RATE_REF_INTERVAL));
3506 
3507     /*
3508      * Divisor ranging from 10, for minimum weight, to 2, for
3509      * maximum weight.
3510      */
3511     divisor = 10 - weight;
3512 
3513     /*
3514      * Finally, update peak rate:
3515      *
3516      * peak_rate = peak_rate * (divisor-1) / divisor  +  rate / divisor
3517      */
3518     bfqd->peak_rate *= divisor-1;
3519     bfqd->peak_rate /= divisor;
3520     rate /= divisor; /* smoothing constant alpha = 1/divisor */
3521 
3522     bfqd->peak_rate += rate;
3523 
3524     /*
3525      * For a very slow device, bfqd->peak_rate can reach 0 (see
3526      * the minimum representable values reported in the comments
3527      * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3528      * divisions by zero where bfqd->peak_rate is used as a
3529      * divisor.
3530      */
3531     bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3532 
3533     update_thr_responsiveness_params(bfqd);
3534 
3535 reset_computation:
3536     bfq_reset_rate_computation(bfqd, rq);
3537 }
3538 
3539 /*
3540  * Update the read/write peak rate (the main quantity used for
3541  * auto-tuning, see update_thr_responsiveness_params()).
3542  *
3543  * It is not trivial to estimate the peak rate (correctly): because of
3544  * the presence of sw and hw queues between the scheduler and the
3545  * device components that finally serve I/O requests, it is hard to
3546  * say exactly when a given dispatched request is served inside the
3547  * device, and for how long. As a consequence, it is hard to know
3548  * precisely at what rate a given set of requests is actually served
3549  * by the device.
3550  *
3551  * On the opposite end, the dispatch time of any request is trivially
3552  * available, and, from this piece of information, the "dispatch rate"
3553  * of requests can be immediately computed. So, the idea in the next
3554  * function is to use what is known, namely request dispatch times
3555  * (plus, when useful, request completion times), to estimate what is
3556  * unknown, namely in-device request service rate.
3557  *
3558  * The main issue is that, because of the above facts, the rate at
3559  * which a certain set of requests is dispatched over a certain time
3560  * interval can vary greatly with respect to the rate at which the
3561  * same requests are then served. But, since the size of any
3562  * intermediate queue is limited, and the service scheme is lossless
3563  * (no request is silently dropped), the following obvious convergence
3564  * property holds: the number of requests dispatched MUST become
3565  * closer and closer to the number of requests completed as the
3566  * observation interval grows. This is the key property used in
3567  * the next function to estimate the peak service rate as a function
3568  * of the observed dispatch rate. The function assumes to be invoked
3569  * on every request dispatch.
3570  */
3571 static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3572 {
3573     u64 now_ns = ktime_get_ns();
3574 
3575     if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3576         bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3577             bfqd->peak_rate_samples);
3578         bfq_reset_rate_computation(bfqd, rq);
3579         goto update_last_values; /* will add one sample */
3580     }
3581 
3582     /*
3583      * Device idle for very long: the observation interval lasting
3584      * up to this dispatch cannot be a valid observation interval
3585      * for computing a new peak rate (similarly to the late-
3586      * completion event in bfq_completed_request()). Go to
3587      * update_rate_and_reset to have the following three steps
3588      * taken:
3589      * - close the observation interval at the last (previous)
3590      *   request dispatch or completion
3591      * - compute rate, if possible, for that observation interval
3592      * - start a new observation interval with this dispatch
3593      */
3594     if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3595         bfqd->rq_in_driver == 0)
3596         goto update_rate_and_reset;
3597 
3598     /* Update sampling information */
3599     bfqd->peak_rate_samples++;
3600 
3601     if ((bfqd->rq_in_driver > 0 ||
3602         now_ns - bfqd->last_completion < BFQ_MIN_TT)
3603         && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3604         bfqd->sequential_samples++;
3605 
3606     bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3607 
3608     /* Reset max observed rq size every 32 dispatches */
3609     if (likely(bfqd->peak_rate_samples % 32))
3610         bfqd->last_rq_max_size =
3611             max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3612     else
3613         bfqd->last_rq_max_size = blk_rq_sectors(rq);
3614 
3615     bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3616 
3617     /* Target observation interval not yet reached, go on sampling */
3618     if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3619         goto update_last_values;
3620 
3621 update_rate_and_reset:
3622     bfq_update_rate_reset(bfqd, rq);
3623 update_last_values:
3624     bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3625     if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3626         bfqd->in_serv_last_pos = bfqd->last_position;
3627     bfqd->last_dispatch = now_ns;
3628 }
3629 
3630 /*
3631  * Remove request from internal lists.
3632  */
3633 static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3634 {
3635     struct bfq_queue *bfqq = RQ_BFQQ(rq);
3636 
3637     /*
3638      * For consistency, the next instruction should have been
3639      * executed after removing the request from the queue and
3640      * dispatching it.  We execute instead this instruction before
3641      * bfq_remove_request() (and hence introduce a temporary
3642      * inconsistency), for efficiency.  In fact, should this
3643      * dispatch occur for a non in-service bfqq, this anticipated
3644      * increment prevents two counters related to bfqq->dispatched
3645      * from risking to be, first, uselessly decremented, and then
3646      * incremented again when the (new) value of bfqq->dispatched
3647      * happens to be taken into account.
3648      */
3649     bfqq->dispatched++;
3650     bfq_update_peak_rate(q->elevator->elevator_data, rq);
3651 
3652     bfq_remove_request(q, rq);
3653 }
3654 
3655 /*
3656  * There is a case where idling does not have to be performed for
3657  * throughput concerns, but to preserve the throughput share of
3658  * the process associated with bfqq.
3659  *
3660  * To introduce this case, we can note that allowing the drive
3661  * to enqueue more than one request at a time, and hence
3662  * delegating de facto final scheduling decisions to the
3663  * drive's internal scheduler, entails loss of control on the
3664  * actual request service order. In particular, the critical
3665  * situation is when requests from different processes happen
3666  * to be present, at the same time, in the internal queue(s)
3667  * of the drive. In such a situation, the drive, by deciding
3668  * the service order of the internally-queued requests, does
3669  * determine also the actual throughput distribution among
3670  * these processes. But the drive typically has no notion or
3671  * concern about per-process throughput distribution, and
3672  * makes its decisions only on a per-request basis. Therefore,
3673  * the service distribution enforced by the drive's internal
3674  * scheduler is likely to coincide with the desired throughput
3675  * distribution only in a completely symmetric, or favorably
3676  * skewed scenario where:
3677  * (i-a) each of these processes must get the same throughput as
3678  *   the others,
3679  * (i-b) in case (i-a) does not hold, it holds that the process
3680  *       associated with bfqq must receive a lower or equal
3681  *   throughput than any of the other processes;
3682  * (ii)  the I/O of each process has the same properties, in
3683  *       terms of locality (sequential or random), direction
3684  *       (reads or writes), request sizes, greediness
3685  *       (from I/O-bound to sporadic), and so on;
3686 
3687  * In fact, in such a scenario, the drive tends to treat the requests
3688  * of each process in about the same way as the requests of the
3689  * others, and thus to provide each of these processes with about the
3690  * same throughput.  This is exactly the desired throughput
3691  * distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3692  * even more convenient distribution for (the process associated with)
3693  * bfqq.
3694  *
3695  * In contrast, in any asymmetric or unfavorable scenario, device
3696  * idling (I/O-dispatch plugging) is certainly needed to guarantee
3697  * that bfqq receives its assigned fraction of the device throughput
3698  * (see [1] for details).
3699  *
3700  * The problem is that idling may significantly reduce throughput with
3701  * certain combinations of types of I/O and devices. An important
3702  * example is sync random I/O on flash storage with command
3703  * queueing. So, unless bfqq falls in cases where idling also boosts
3704  * throughput, it is important to check conditions (i-a), i(-b) and
3705  * (ii) accurately, so as to avoid idling when not strictly needed for
3706  * service guarantees.
3707  *
3708  * Unfortunately, it is extremely difficult to thoroughly check
3709  * condition (ii). And, in case there are active groups, it becomes
3710  * very difficult to check conditions (i-a) and (i-b) too.  In fact,
3711  * if there are active groups, then, for conditions (i-a) or (i-b) to
3712  * become false 'indirectly', it is enough that an active group
3713  * contains more active processes or sub-groups than some other active
3714  * group. More precisely, for conditions (i-a) or (i-b) to become
3715  * false because of such a group, it is not even necessary that the
3716  * group is (still) active: it is sufficient that, even if the group
3717  * has become inactive, some of its descendant processes still have
3718  * some request already dispatched but still waiting for
3719  * completion. In fact, requests have still to be guaranteed their
3720  * share of the throughput even after being dispatched. In this
3721  * respect, it is easy to show that, if a group frequently becomes
3722  * inactive while still having in-flight requests, and if, when this
3723  * happens, the group is not considered in the calculation of whether
3724  * the scenario is asymmetric, then the group may fail to be
3725  * guaranteed its fair share of the throughput (basically because
3726  * idling may not be performed for the descendant processes of the
3727  * group, but it had to be).  We address this issue with the following
3728  * bi-modal behavior, implemented in the function
3729  * bfq_asymmetric_scenario().
3730  *
3731  * If there are groups with requests waiting for completion
3732  * (as commented above, some of these groups may even be
3733  * already inactive), then the scenario is tagged as
3734  * asymmetric, conservatively, without checking any of the
3735  * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3736  * This behavior matches also the fact that groups are created
3737  * exactly if controlling I/O is a primary concern (to
3738  * preserve bandwidth and latency guarantees).
3739  *
3740  * On the opposite end, if there are no groups with requests waiting
3741  * for completion, then only conditions (i-a) and (i-b) are actually
3742  * controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3743  * idling is not performed, regardless of whether condition (ii)
3744  * holds.  In other words, only if conditions (i-a) and (i-b) do not
3745  * hold, then idling is allowed, and the device tends to be prevented
3746  * from queueing many requests, possibly of several processes. Since
3747  * there are no groups with requests waiting for completion, then, to
3748  * control conditions (i-a) and (i-b) it is enough to check just
3749  * whether all the queues with requests waiting for completion also
3750  * have the same weight.
3751  *
3752  * Not checking condition (ii) evidently exposes bfqq to the
3753  * risk of getting less throughput than its fair share.
3754  * However, for queues with the same weight, a further
3755  * mechanism, preemption, mitigates or even eliminates this
3756  * problem. And it does so without consequences on overall
3757  * throughput. This mechanism and its benefits are explained
3758  * in the next three paragraphs.
3759  *
3760  * Even if a queue, say Q, is expired when it remains idle, Q
3761  * can still preempt the new in-service queue if the next
3762  * request of Q arrives soon (see the comments on
3763  * bfq_bfqq_update_budg_for_activation). If all queues and
3764  * groups have the same weight, this form of preemption,
3765  * combined with the hole-recovery heuristic described in the
3766  * comments on function bfq_bfqq_update_budg_for_activation,
3767  * are enough to preserve a correct bandwidth distribution in
3768  * the mid term, even without idling. In fact, even if not
3769  * idling allows the internal queues of the device to contain
3770  * many requests, and thus to reorder requests, we can rather
3771  * safely assume that the internal scheduler still preserves a
3772  * minimum of mid-term fairness.
3773  *
3774  * More precisely, this preemption-based, idleless approach
3775  * provides fairness in terms of IOPS, and not sectors per
3776  * second. This can be seen with a simple example. Suppose
3777  * that there are two queues with the same weight, but that
3778  * the first queue receives requests of 8 sectors, while the
3779  * second queue receives requests of 1024 sectors. In
3780  * addition, suppose that each of the two queues contains at
3781  * most one request at a time, which implies that each queue
3782  * always remains idle after it is served. Finally, after
3783  * remaining idle, each queue receives very quickly a new
3784  * request. It follows that the two queues are served
3785  * alternatively, preempting each other if needed. This
3786  * implies that, although both queues have the same weight,
3787  * the queue with large requests receives a service that is
3788  * 1024/8 times as high as the service received by the other
3789  * queue.
3790  *
3791  * The motivation for using preemption instead of idling (for
3792  * queues with the same weight) is that, by not idling,
3793  * service guarantees are preserved (completely or at least in
3794  * part) without minimally sacrificing throughput. And, if
3795  * there is no active group, then the primary expectation for
3796  * this device is probably a high throughput.
3797  *
3798  * We are now left only with explaining the two sub-conditions in the
3799  * additional compound condition that is checked below for deciding
3800  * whether the scenario is asymmetric. To explain the first
3801  * sub-condition, we need to add that the function
3802  * bfq_asymmetric_scenario checks the weights of only
3803  * non-weight-raised queues, for efficiency reasons (see comments on
3804  * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3805  * is checked explicitly here. More precisely, the compound condition
3806  * below takes into account also the fact that, even if bfqq is being
3807  * weight-raised, the scenario is still symmetric if all queues with
3808  * requests waiting for completion happen to be
3809  * weight-raised. Actually, we should be even more precise here, and
3810  * differentiate between interactive weight raising and soft real-time
3811  * weight raising.
3812  *
3813  * The second sub-condition checked in the compound condition is
3814  * whether there is a fair amount of already in-flight I/O not
3815  * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3816  * following reason. The drive may decide to serve in-flight
3817  * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3818  * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3819  * I/O-dispatching is not plugged, then, while bfqq remains empty, a
3820  * basically uncontrolled amount of I/O from other queues may be
3821  * dispatched too, possibly causing the service of bfqq's I/O to be
3822  * delayed even longer in the drive. This problem gets more and more
3823  * serious as the speed and the queue depth of the drive grow,
3824  * because, as these two quantities grow, the probability to find no
3825  * queue busy but many requests in flight grows too. By contrast,
3826  * plugging I/O dispatching minimizes the delay induced by already
3827  * in-flight I/O, and enables bfqq to recover the bandwidth it may
3828  * lose because of this delay.
3829  *
3830  * As a side note, it is worth considering that the above
3831  * device-idling countermeasures may however fail in the following
3832  * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3833  * in a time period during which all symmetry sub-conditions hold, and
3834  * therefore the device is allowed to enqueue many requests, but at
3835  * some later point in time some sub-condition stops to hold, then it
3836  * may become impossible to make requests be served in the desired
3837  * order until all the requests already queued in the device have been
3838  * served. The last sub-condition commented above somewhat mitigates
3839  * this problem for weight-raised queues.
3840  *
3841  * However, as an additional mitigation for this problem, we preserve
3842  * plugging for a special symmetric case that may suddenly turn into
3843  * asymmetric: the case where only bfqq is busy. In this case, not
3844  * expiring bfqq does not cause any harm to any other queues in terms
3845  * of service guarantees. In contrast, it avoids the following unlucky
3846  * sequence of events: (1) bfqq is expired, (2) a new queue with a
3847  * lower weight than bfqq becomes busy (or more queues), (3) the new
3848  * queue is served until a new request arrives for bfqq, (4) when bfqq
3849  * is finally served, there are so many requests of the new queue in
3850  * the drive that the pending requests for bfqq take a lot of time to
3851  * be served. In particular, event (2) may case even already
3852  * dispatched requests of bfqq to be delayed, inside the drive. So, to
3853  * avoid this series of events, the scenario is preventively declared
3854  * as asymmetric also if bfqq is the only busy queues
3855  */
3856 static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3857                          struct bfq_queue *bfqq)
3858 {
3859     int tot_busy_queues = bfq_tot_busy_queues(bfqd);
3860 
3861     /* No point in idling for bfqq if it won't get requests any longer */
3862     if (unlikely(!bfqq_process_refs(bfqq)))
3863         return false;
3864 
3865     return (bfqq->wr_coeff > 1 &&
3866         (bfqd->wr_busy_queues <
3867          tot_busy_queues ||
3868          bfqd->rq_in_driver >=
3869          bfqq->dispatched + 4)) ||
3870         bfq_asymmetric_scenario(bfqd, bfqq) ||
3871         tot_busy_queues == 1;
3872 }
3873 
3874 static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3875                   enum bfqq_expiration reason)
3876 {
3877     /*
3878      * If this bfqq is shared between multiple processes, check
3879      * to make sure that those processes are still issuing I/Os
3880      * within the mean seek distance. If not, it may be time to
3881      * break the queues apart again.
3882      */
3883     if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3884         bfq_mark_bfqq_split_coop(bfqq);
3885 
3886     /*
3887      * Consider queues with a higher finish virtual time than
3888      * bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3889      * true, then bfqq's bandwidth would be violated if an
3890      * uncontrolled amount of I/O from these queues were
3891      * dispatched while bfqq is waiting for its new I/O to
3892      * arrive. This is exactly what may happen if this is a forced
3893      * expiration caused by a preemption attempt, and if bfqq is
3894      * not re-scheduled. To prevent this from happening, re-queue
3895      * bfqq if it needs I/O-dispatch plugging, even if it is
3896      * empty. By doing so, bfqq is granted to be served before the
3897      * above queues (provided that bfqq is of course eligible).
3898      */
3899     if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3900         !(reason == BFQQE_PREEMPTED &&
3901           idling_needed_for_service_guarantees(bfqd, bfqq))) {
3902         if (bfqq->dispatched == 0)
3903             /*
3904              * Overloading budget_timeout field to store
3905              * the time at which the queue remains with no
3906              * backlog and no outstanding request; used by
3907              * the weight-raising mechanism.
3908              */
3909             bfqq->budget_timeout = jiffies;
3910 
3911         bfq_del_bfqq_busy(bfqd, bfqq, true);
3912     } else {
3913         bfq_requeue_bfqq(bfqd, bfqq, true);
3914         /*
3915          * Resort priority tree of potential close cooperators.
3916          * See comments on bfq_pos_tree_add_move() for the unlikely().
3917          */
3918         if (unlikely(!bfqd->nonrot_with_queueing &&
3919                  !RB_EMPTY_ROOT(&bfqq->sort_list)))
3920             bfq_pos_tree_add_move(bfqd, bfqq);
3921     }
3922 
3923     /*
3924      * All in-service entities must have been properly deactivated
3925      * or requeued before executing the next function, which
3926      * resets all in-service entities as no more in service. This
3927      * may cause bfqq to be freed. If this happens, the next
3928      * function returns true.
3929      */
3930     return __bfq_bfqd_reset_in_service(bfqd);
3931 }
3932 
3933 /**
3934  * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3935  * @bfqd: device data.
3936  * @bfqq: queue to update.
3937  * @reason: reason for expiration.
3938  *
3939  * Handle the feedback on @bfqq budget at queue expiration.
3940  * See the body for detailed comments.
3941  */
3942 static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3943                      struct bfq_queue *bfqq,
3944                      enum bfqq_expiration reason)
3945 {
3946     struct request *next_rq;
3947     int budget, min_budget;
3948 
3949     min_budget = bfq_min_budget(bfqd);
3950 
3951     if (bfqq->wr_coeff == 1)
3952         budget = bfqq->max_budget;
3953     else /*
3954           * Use a constant, low budget for weight-raised queues,
3955           * to help achieve a low latency. Keep it slightly higher
3956           * than the minimum possible budget, to cause a little
3957           * bit fewer expirations.
3958           */
3959         budget = 2 * min_budget;
3960 
3961     bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3962         bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3963     bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3964         budget, bfq_min_budget(bfqd));
3965     bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3966         bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3967 
3968     if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3969         switch (reason) {
3970         /*
3971          * Caveat: in all the following cases we trade latency
3972          * for throughput.
3973          */
3974         case BFQQE_TOO_IDLE:
3975             /*
3976              * This is the only case where we may reduce
3977              * the budget: if there is no request of the
3978              * process still waiting for completion, then
3979              * we assume (tentatively) that the timer has
3980              * expired because the batch of requests of
3981              * the process could have been served with a
3982              * smaller budget.  Hence, betting that
3983              * process will behave in the same way when it
3984              * becomes backlogged again, we reduce its
3985              * next budget.  As long as we guess right,
3986              * this budget cut reduces the latency
3987              * experienced by the process.
3988              *
3989              * However, if there are still outstanding
3990              * requests, then the process may have not yet
3991              * issued its next request just because it is
3992              * still waiting for the completion of some of
3993              * the still outstanding ones.  So in this
3994              * subcase we do not reduce its budget, on the
3995              * contrary we increase it to possibly boost
3996              * the throughput, as discussed in the
3997              * comments to the BUDGET_TIMEOUT case.
3998              */
3999             if (bfqq->dispatched > 0) /* still outstanding reqs */
4000                 budget = min(budget * 2, bfqd->bfq_max_budget);
4001             else {
4002                 if (budget > 5 * min_budget)
4003                     budget -= 4 * min_budget;
4004                 else
4005                     budget = min_budget;
4006             }
4007             break;
4008         case BFQQE_BUDGET_TIMEOUT:
4009             /*
4010              * We double the budget here because it gives
4011              * the chance to boost the throughput if this
4012              * is not a seeky process (and has bumped into
4013              * this timeout because of, e.g., ZBR).
4014              */
4015             budget = min(budget * 2, bfqd->bfq_max_budget);
4016             break;
4017         case BFQQE_BUDGET_EXHAUSTED:
4018             /*
4019              * The process still has backlog, and did not
4020              * let either the budget timeout or the disk
4021              * idling timeout expire. Hence it is not
4022              * seeky, has a short thinktime and may be
4023              * happy with a higher budget too. So
4024              * definitely increase the budget of this good
4025              * candidate to boost the disk throughput.
4026              */
4027             budget = min(budget * 4, bfqd->bfq_max_budget);
4028             break;
4029         case BFQQE_NO_MORE_REQUESTS:
4030             /*
4031              * For queues that expire for this reason, it
4032              * is particularly important to keep the
4033              * budget close to the actual service they
4034              * need. Doing so reduces the timestamp
4035              * misalignment problem described in the
4036              * comments in the body of
4037              * __bfq_activate_entity. In fact, suppose
4038              * that a queue systematically expires for
4039              * BFQQE_NO_MORE_REQUESTS and presents a
4040              * new request in time to enjoy timestamp
4041              * back-shifting. The larger the budget of the
4042              * queue is with respect to the service the
4043              * queue actually requests in each service
4044              * slot, the more times the queue can be
4045              * reactivated with the same virtual finish
4046              * time. It follows that, even if this finish
4047              * time is pushed to the system virtual time
4048              * to reduce the consequent timestamp
4049              * misalignment, the queue unjustly enjoys for
4050              * many re-activations a lower finish time
4051              * than all newly activated queues.
4052              *
4053              * The service needed by bfqq is measured
4054              * quite precisely by bfqq->entity.service.
4055              * Since bfqq does not enjoy device idling,
4056              * bfqq->entity.service is equal to the number
4057              * of sectors that the process associated with
4058              * bfqq requested to read/write before waiting
4059              * for request completions, or blocking for
4060              * other reasons.
4061              */
4062             budget = max_t(int, bfqq->entity.service, min_budget);
4063             break;
4064         default:
4065             return;
4066         }
4067     } else if (!bfq_bfqq_sync(bfqq)) {
4068         /*
4069          * Async queues get always the maximum possible
4070          * budget, as for them we do not care about latency
4071          * (in addition, their ability to dispatch is limited
4072          * by the charging factor).
4073          */
4074         budget = bfqd->bfq_max_budget;
4075     }
4076 
4077     bfqq->max_budget = budget;
4078 
4079     if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
4080         !bfqd->bfq_user_max_budget)
4081         bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
4082 
4083     /*
4084      * If there is still backlog, then assign a new budget, making
4085      * sure that it is large enough for the next request.  Since
4086      * the finish time of bfqq must be kept in sync with the
4087      * budget, be sure to call __bfq_bfqq_expire() *after* this
4088      * update.
4089      *
4090      * If there is no backlog, then no need to update the budget;
4091      * it will be updated on the arrival of a new request.
4092      */
4093     next_rq = bfqq->next_rq;
4094     if (next_rq)
4095         bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
4096                         bfq_serv_to_charge(next_rq, bfqq));
4097 
4098     bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
4099             next_rq ? blk_rq_sectors(next_rq) : 0,
4100             bfqq->entity.budget);
4101 }
4102 
4103 /*
4104  * Return true if the process associated with bfqq is "slow". The slow
4105  * flag is used, in addition to the budget timeout, to reduce the
4106  * amount of service provided to seeky processes, and thus reduce
4107  * their chances to lower the throughput. More details in the comments
4108  * on the function bfq_bfqq_expire().
4109  *
4110  * An important observation is in order: as discussed in the comments
4111  * on the function bfq_update_peak_rate(), with devices with internal
4112  * queues, it is hard if ever possible to know when and for how long
4113  * an I/O request is processed by the device (apart from the trivial
4114  * I/O pattern where a new request is dispatched only after the
4115  * previous one has been completed). This makes it hard to evaluate
4116  * the real rate at which the I/O requests of each bfq_queue are
4117  * served.  In fact, for an I/O scheduler like BFQ, serving a
4118  * bfq_queue means just dispatching its requests during its service
4119  * slot (i.e., until the budget of the queue is exhausted, or the
4120  * queue remains idle, or, finally, a timeout fires). But, during the
4121  * service slot of a bfq_queue, around 100 ms at most, the device may
4122  * be even still processing requests of bfq_queues served in previous
4123  * service slots. On the opposite end, the requests of the in-service
4124  * bfq_queue may be completed after the service slot of the queue
4125  * finishes.
4126  *
4127  * Anyway, unless more sophisticated solutions are used
4128  * (where possible), the sum of the sizes of the requests dispatched
4129  * during the service slot of a bfq_queue is probably the only
4130  * approximation available for the service received by the bfq_queue
4131  * during its service slot. And this sum is the quantity used in this
4132  * function to evaluate the I/O speed of a process.
4133  */
4134 static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4135                  bool compensate, enum bfqq_expiration reason,
4136                  unsigned long *delta_ms)
4137 {
4138     ktime_t delta_ktime;
4139     u32 delta_usecs;
4140     bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
4141 
4142     if (!bfq_bfqq_sync(bfqq))
4143         return false;
4144 
4145     if (compensate)
4146         delta_ktime = bfqd->last_idling_start;
4147     else
4148         delta_ktime = ktime_get();
4149     delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
4150     delta_usecs = ktime_to_us(delta_ktime);
4151 
4152     /* don't use too short time intervals */
4153     if (delta_usecs < 1000) {
4154         if (blk_queue_nonrot(bfqd->queue))
4155              /*
4156               * give same worst-case guarantees as idling
4157               * for seeky
4158               */
4159             *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
4160         else /* charge at least one seek */
4161             *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
4162 
4163         return slow;
4164     }
4165 
4166     *delta_ms = delta_usecs / USEC_PER_MSEC;
4167 
4168     /*
4169      * Use only long (> 20ms) intervals to filter out excessive
4170      * spikes in service rate estimation.
4171      */
4172     if (delta_usecs > 20000) {
4173         /*
4174          * Caveat for rotational devices: processes doing I/O
4175          * in the slower disk zones tend to be slow(er) even
4176          * if not seeky. In this respect, the estimated peak
4177          * rate is likely to be an average over the disk
4178          * surface. Accordingly, to not be too harsh with
4179          * unlucky processes, a process is deemed slow only if
4180          * its rate has been lower than half of the estimated
4181          * peak rate.
4182          */
4183         slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
4184     }
4185 
4186     bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
4187 
4188     return slow;
4189 }
4190 
4191 /*
4192  * To be deemed as soft real-time, an application must meet two
4193  * requirements. First, the application must not require an average
4194  * bandwidth higher than the approximate bandwidth required to playback or
4195  * record a compressed high-definition video.
4196  * The next function is invoked on the completion of the last request of a
4197  * batch, to compute the next-start time instant, soft_rt_next_start, such
4198  * that, if the next request of the application does not arrive before
4199  * soft_rt_next_start, then the above requirement on the bandwidth is met.
4200  *
4201  * The second requirement is that the request pattern of the application is
4202  * isochronous, i.e., that, after issuing a request or a batch of requests,
4203  * the application stops issuing new requests until all its pending requests
4204  * have been completed. After that, the application may issue a new batch,
4205  * and so on.
4206  * For this reason the next function is invoked to compute
4207  * soft_rt_next_start only for applications that meet this requirement,
4208  * whereas soft_rt_next_start is set to infinity for applications that do
4209  * not.
4210  *
4211  * Unfortunately, even a greedy (i.e., I/O-bound) application may
4212  * happen to meet, occasionally or systematically, both the above
4213  * bandwidth and isochrony requirements. This may happen at least in
4214  * the following circumstances. First, if the CPU load is high. The
4215  * application may stop issuing requests while the CPUs are busy
4216  * serving other processes, then restart, then stop again for a while,
4217  * and so on. The other circumstances are related to the storage
4218  * device: the storage device is highly loaded or reaches a low-enough
4219  * throughput with the I/O of the application (e.g., because the I/O
4220  * is random and/or the device is slow). In all these cases, the
4221  * I/O of the application may be simply slowed down enough to meet
4222  * the bandwidth and isochrony requirements. To reduce the probability
4223  * that greedy applications are deemed as soft real-time in these
4224  * corner cases, a further rule is used in the computation of
4225  * soft_rt_next_start: the return value of this function is forced to
4226  * be higher than the maximum between the following two quantities.
4227  *
4228  * (a) Current time plus: (1) the maximum time for which the arrival
4229  *     of a request is waited for when a sync queue becomes idle,
4230  *     namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
4231  *     postpone for a moment the reason for adding a few extra
4232  *     jiffies; we get back to it after next item (b).  Lower-bounding
4233  *     the return value of this function with the current time plus
4234  *     bfqd->bfq_slice_idle tends to filter out greedy applications,
4235  *     because the latter issue their next request as soon as possible
4236  *     after the last one has been completed. In contrast, a soft
4237  *     real-time application spends some time processing data, after a
4238  *     batch of its requests has been completed.
4239  *
4240  * (b) Current value of bfqq->soft_rt_next_start. As pointed out
4241  *     above, greedy applications may happen to meet both the
4242  *     bandwidth and isochrony requirements under heavy CPU or
4243  *     storage-device load. In more detail, in these scenarios, these
4244  *     applications happen, only for limited time periods, to do I/O
4245  *     slowly enough to meet all the requirements described so far,
4246  *     including the filtering in above item (a). These slow-speed
4247  *     time intervals are usually interspersed between other time
4248  *     intervals during which these applications do I/O at a very high
4249  *     speed. Fortunately, exactly because of the high speed of the
4250  *     I/O in the high-speed intervals, the values returned by this
4251  *     function happen to be so high, near the end of any such
4252  *     high-speed interval, to be likely to fall *after* the end of
4253  *     the low-speed time interval that follows. These high values are
4254  *     stored in bfqq->soft_rt_next_start after each invocation of
4255  *     this function. As a consequence, if the last value of
4256  *     bfqq->soft_rt_next_start is constantly used to lower-bound the
4257  *     next value that this function may return, then, from the very
4258  *     beginning of a low-speed interval, bfqq->soft_rt_next_start is
4259  *     likely to be constantly kept so high that any I/O request
4260  *     issued during the low-speed interval is considered as arriving
4261  *     to soon for the application to be deemed as soft
4262  *     real-time. Then, in the high-speed interval that follows, the
4263  *     application will not be deemed as soft real-time, just because
4264  *     it will do I/O at a high speed. And so on.
4265  *
4266  * Getting back to the filtering in item (a), in the following two
4267  * cases this filtering might be easily passed by a greedy
4268  * application, if the reference quantity was just
4269  * bfqd->bfq_slice_idle:
4270  * 1) HZ is so low that the duration of a jiffy is comparable to or
4271  *    higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
4272  *    devices with HZ=100. The time granularity may be so coarse
4273  *    that the approximation, in jiffies, of bfqd->bfq_slice_idle
4274  *    is rather lower than the exact value.
4275  * 2) jiffies, instead of increasing at a constant rate, may stop increasing
4276  *    for a while, then suddenly 'jump' by several units to recover the lost
4277  *    increments. This seems to happen, e.g., inside virtual machines.
4278  * To address this issue, in the filtering in (a) we do not use as a
4279  * reference time interval just bfqd->bfq_slice_idle, but
4280  * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
4281  * minimum number of jiffies for which the filter seems to be quite
4282  * precise also in embedded systems and KVM/QEMU virtual machines.
4283  */
4284 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
4285                         struct bfq_queue *bfqq)
4286 {
4287     return max3(bfqq->soft_rt_next_start,
4288             bfqq->last_idle_bklogged +
4289             HZ * bfqq->service_from_backlogged /
4290             bfqd->bfq_wr_max_softrt_rate,
4291             jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
4292 }
4293 
4294 /**
4295  * bfq_bfqq_expire - expire a queue.
4296  * @bfqd: device owning the queue.
4297  * @bfqq: the queue to expire.
4298  * @compensate: if true, compensate for the time spent idling.
4299  * @reason: the reason causing the expiration.
4300  *
4301  * If the process associated with bfqq does slow I/O (e.g., because it
4302  * issues random requests), we charge bfqq with the time it has been
4303  * in service instead of the service it has received (see
4304  * bfq_bfqq_charge_time for details on how this goal is achieved). As
4305  * a consequence, bfqq will typically get higher timestamps upon
4306  * reactivation, and hence it will be rescheduled as if it had
4307  * received more service than what it has actually received. In the
4308  * end, bfqq receives less service in proportion to how slowly its
4309  * associated process consumes its budgets (and hence how seriously it
4310  * tends to lower the throughput). In addition, this time-charging
4311  * strategy guarantees time fairness among slow processes. In
4312  * contrast, if the process associated with bfqq is not slow, we
4313  * charge bfqq exactly with the service it has received.
4314  *
4315  * Charging time to the first type of queues and the exact service to
4316  * the other has the effect of using the WF2Q+ policy to schedule the
4317  * former on a timeslice basis, without violating service domain
4318  * guarantees among the latter.
4319  */
4320 void bfq_bfqq_expire(struct bfq_data *bfqd,
4321              struct bfq_queue *bfqq,
4322              bool compensate,
4323              enum bfqq_expiration reason)
4324 {
4325     bool slow;
4326     unsigned long delta = 0;
4327     struct bfq_entity *entity = &bfqq->entity;
4328 
4329     /*
4330      * Check whether the process is slow (see bfq_bfqq_is_slow).
4331      */
4332     slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
4333 
4334     /*
4335      * As above explained, charge slow (typically seeky) and
4336      * timed-out queues with the time and not the service
4337      * received, to favor sequential workloads.
4338      *
4339      * Processes doing I/O in the slower disk zones will tend to
4340      * be slow(er) even if not seeky. Therefore, since the
4341      * estimated peak rate is actually an average over the disk
4342      * surface, these processes may timeout just for bad luck. To
4343      * avoid punishing them, do not charge time to processes that
4344      * succeeded in consuming at least 2/3 of their budget. This
4345      * allows BFQ to preserve enough elasticity to still perform
4346      * bandwidth, and not time, distribution with little unlucky
4347      * or quasi-sequential processes.
4348      */
4349     if (bfqq->wr_coeff == 1 &&
4350         (slow ||
4351          (reason == BFQQE_BUDGET_TIMEOUT &&
4352           bfq_bfqq_budget_left(bfqq) >=  entity->budget / 3)))
4353         bfq_bfqq_charge_time(bfqd, bfqq, delta);
4354 
4355     if (bfqd->low_latency && bfqq->wr_coeff == 1)
4356         bfqq->last_wr_start_finish = jiffies;
4357 
4358     if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
4359         RB_EMPTY_ROOT(&bfqq->sort_list)) {
4360         /*
4361          * If we get here, and there are no outstanding
4362          * requests, then the request pattern is isochronous
4363          * (see the comments on the function
4364          * bfq_bfqq_softrt_next_start()). Therefore we can
4365          * compute soft_rt_next_start.
4366          *
4367          * If, instead, the queue still has outstanding
4368          * requests, then we have to wait for the completion
4369          * of all the outstanding requests to discover whether
4370          * the request pattern is actually isochronous.
4371          */
4372         if (bfqq->dispatched == 0)
4373             bfqq->soft_rt_next_start =
4374                 bfq_bfqq_softrt_next_start(bfqd, bfqq);
4375         else if (bfqq->dispatched > 0) {
4376             /*
4377              * Schedule an update of soft_rt_next_start to when
4378              * the task may be discovered to be isochronous.
4379              */
4380             bfq_mark_bfqq_softrt_update(bfqq);
4381         }
4382     }
4383 
4384     bfq_log_bfqq(bfqd, bfqq,
4385         "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
4386         slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
4387 
4388     /*
4389      * bfqq expired, so no total service time needs to be computed
4390      * any longer: reset state machine for measuring total service
4391      * times.
4392      */
4393     bfqd->rqs_injected = bfqd->wait_dispatch = false;
4394     bfqd->waited_rq = NULL;
4395 
4396     /*
4397      * Increase, decrease or leave budget unchanged according to
4398      * reason.
4399      */
4400     __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4401     if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4402         /* bfqq is gone, no more actions on it */
4403         return;
4404 
4405     /* mark bfqq as waiting a request only if a bic still points to it */
4406     if (!bfq_bfqq_busy(bfqq) &&
4407         reason != BFQQE_BUDGET_TIMEOUT &&
4408         reason != BFQQE_BUDGET_EXHAUSTED) {
4409         bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4410         /*
4411          * Not setting service to 0, because, if the next rq
4412          * arrives in time, the queue will go on receiving
4413          * service with this same budget (as if it never expired)
4414          */
4415     } else
4416         entity->service = 0;
4417 
4418     /*
4419      * Reset the received-service counter for every parent entity.
4420      * Differently from what happens with bfqq->entity.service,
4421      * the resetting of this counter never needs to be postponed
4422      * for parent entities. In fact, in case bfqq may have a
4423      * chance to go on being served using the last, partially
4424      * consumed budget, bfqq->entity.service needs to be kept,
4425      * because if bfqq then actually goes on being served using
4426      * the same budget, the last value of bfqq->entity.service is
4427      * needed to properly decrement bfqq->entity.budget by the
4428      * portion already consumed. In contrast, it is not necessary
4429      * to keep entity->service for parent entities too, because
4430      * the bubble up of the new value of bfqq->entity.budget will
4431      * make sure that the budgets of parent entities are correct,
4432      * even in case bfqq and thus parent entities go on receiving
4433      * service with the same budget.
4434      */
4435     entity = entity->parent;
4436     for_each_entity(entity)
4437         entity->service = 0;
4438 }
4439 
4440 /*
4441  * Budget timeout is not implemented through a dedicated timer, but
4442  * just checked on request arrivals and completions, as well as on
4443  * idle timer expirations.
4444  */
4445 static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4446 {
4447     return time_is_before_eq_jiffies(bfqq->budget_timeout);
4448 }
4449 
4450 /*
4451  * If we expire a queue that is actively waiting (i.e., with the
4452  * device idled) for the arrival of a new request, then we may incur
4453  * the timestamp misalignment problem described in the body of the
4454  * function __bfq_activate_entity. Hence we return true only if this
4455  * condition does not hold, or if the queue is slow enough to deserve
4456  * only to be kicked off for preserving a high throughput.
4457  */
4458 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4459 {
4460     bfq_log_bfqq(bfqq->bfqd, bfqq,
4461         "may_budget_timeout: wait_request %d left %d timeout %d",
4462         bfq_bfqq_wait_request(bfqq),
4463             bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3,
4464         bfq_bfqq_budget_timeout(bfqq));
4465 
4466     return (!bfq_bfqq_wait_request(bfqq) ||
4467         bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3)
4468         &&
4469         bfq_bfqq_budget_timeout(bfqq);
4470 }
4471 
4472 static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4473                          struct bfq_queue *bfqq)
4474 {
4475     bool rot_without_queueing =
4476         !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4477         bfqq_sequential_and_IO_bound,
4478         idling_boosts_thr;
4479 
4480     /* No point in idling for bfqq if it won't get requests any longer */
4481     if (unlikely(!bfqq_process_refs(bfqq)))
4482         return false;
4483 
4484     bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4485         bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4486 
4487     /*
4488      * The next variable takes into account the cases where idling
4489      * boosts the throughput.
4490      *
4491      * The value of the variable is computed considering, first, that
4492      * idling is virtually always beneficial for the throughput if:
4493      * (a) the device is not NCQ-capable and rotational, or
4494      * (b) regardless of the presence of NCQ, the device is rotational and
4495      *     the request pattern for bfqq is I/O-bound and sequential, or
4496      * (c) regardless of whether it is rotational, the device is
4497      *     not NCQ-capable and the request pattern for bfqq is
4498      *     I/O-bound and sequential.
4499      *
4500      * Secondly, and in contrast to the above item (b), idling an
4501      * NCQ-capable flash-based device would not boost the
4502      * throughput even with sequential I/O; rather it would lower
4503      * the throughput in proportion to how fast the device
4504      * is. Accordingly, the next variable is true if any of the
4505      * above conditions (a), (b) or (c) is true, and, in
4506      * particular, happens to be false if bfqd is an NCQ-capable
4507      * flash-based device.
4508      */
4509     idling_boosts_thr = rot_without_queueing ||
4510         ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4511          bfqq_sequential_and_IO_bound);
4512 
4513     /*
4514      * The return value of this function is equal to that of
4515      * idling_boosts_thr, unless a special case holds. In this
4516      * special case, described below, idling may cause problems to
4517      * weight-raised queues.
4518      *
4519      * When the request pool is saturated (e.g., in the presence
4520      * of write hogs), if the processes associated with
4521      * non-weight-raised queues ask for requests at a lower rate,
4522      * then processes associated with weight-raised queues have a
4523      * higher probability to get a request from the pool
4524      * immediately (or at least soon) when they need one. Thus
4525      * they have a higher probability to actually get a fraction
4526      * of the device throughput proportional to their high
4527      * weight. This is especially true with NCQ-capable drives,
4528      * which enqueue several requests in advance, and further
4529      * reorder internally-queued requests.
4530      *
4531      * For this reason, we force to false the return value if
4532      * there are weight-raised busy queues. In this case, and if
4533      * bfqq is not weight-raised, this guarantees that the device
4534      * is not idled for bfqq (if, instead, bfqq is weight-raised,
4535      * then idling will be guaranteed by another variable, see
4536      * below). Combined with the timestamping rules of BFQ (see
4537      * [1] for details), this behavior causes bfqq, and hence any
4538      * sync non-weight-raised queue, to get a lower number of
4539      * requests served, and thus to ask for a lower number of
4540      * requests from the request pool, before the busy
4541      * weight-raised queues get served again. This often mitigates
4542      * starvation problems in the presence of heavy write
4543      * workloads and NCQ, thereby guaranteeing a higher
4544      * application and system responsiveness in these hostile
4545      * scenarios.
4546      */
4547     return idling_boosts_thr &&
4548         bfqd->wr_busy_queues == 0;
4549 }
4550 
4551 /*
4552  * For a queue that becomes empty, device idling is allowed only if
4553  * this function returns true for that queue. As a consequence, since
4554  * device idling plays a critical role for both throughput boosting
4555  * and service guarantees, the return value of this function plays a
4556  * critical role as well.
4557  *
4558  * In a nutshell, this function returns true only if idling is
4559  * beneficial for throughput or, even if detrimental for throughput,
4560  * idling is however necessary to preserve service guarantees (low
4561  * latency, desired throughput distribution, ...). In particular, on
4562  * NCQ-capable devices, this function tries to return false, so as to
4563  * help keep the drives' internal queues full, whenever this helps the
4564  * device boost the throughput without causing any service-guarantee
4565  * issue.
4566  *
4567  * Most of the issues taken into account to get the return value of
4568  * this function are not trivial. We discuss these issues in the two
4569  * functions providing the main pieces of information needed by this
4570  * function.
4571  */
4572 static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4573 {
4574     struct bfq_data *bfqd = bfqq->bfqd;
4575     bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4576 
4577     /* No point in idling for bfqq if it won't get requests any longer */
4578     if (unlikely(!bfqq_process_refs(bfqq)))
4579         return false;
4580 
4581     if (unlikely(bfqd->strict_guarantees))
4582         return true;
4583 
4584     /*
4585      * Idling is performed only if slice_idle > 0. In addition, we
4586      * do not idle if
4587      * (a) bfqq is async
4588      * (b) bfqq is in the idle io prio class: in this case we do
4589      * not idle because we want to minimize the bandwidth that
4590      * queues in this class can steal to higher-priority queues
4591      */
4592     if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4593        bfq_class_idle(bfqq))
4594         return false;
4595 
4596     idling_boosts_thr_with_no_issue =
4597         idling_boosts_thr_without_issues(bfqd, bfqq);
4598 
4599     idling_needed_for_service_guar =
4600         idling_needed_for_service_guarantees(bfqd, bfqq);
4601 
4602     /*
4603      * We have now the two components we need to compute the
4604      * return value of the function, which is true only if idling
4605      * either boosts the throughput (without issues), or is
4606      * necessary to preserve service guarantees.
4607      */
4608     return idling_boosts_thr_with_no_issue ||
4609         idling_needed_for_service_guar;
4610 }
4611 
4612 /*
4613  * If the in-service queue is empty but the function bfq_better_to_idle
4614  * returns true, then:
4615  * 1) the queue must remain in service and cannot be expired, and
4616  * 2) the device must be idled to wait for the possible arrival of a new
4617  *    request for the queue.
4618  * See the comments on the function bfq_better_to_idle for the reasons
4619  * why performing device idling is the best choice to boost the throughput
4620  * and preserve service guarantees when bfq_better_to_idle itself
4621  * returns true.
4622  */
4623 static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4624 {
4625     return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4626 }
4627 
4628 /*
4629  * This function chooses the queue from which to pick the next extra
4630  * I/O request to inject, if it finds a compatible queue. See the
4631  * comments on bfq_update_inject_limit() for details on the injection
4632  * mechanism, and for the definitions of the quantities mentioned
4633  * below.
4634  */
4635 static struct bfq_queue *
4636 bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4637 {
4638     struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4639     unsigned int limit = in_serv_bfqq->inject_limit;
4640     /*
4641      * If
4642      * - bfqq is not weight-raised and therefore does not carry
4643      *   time-critical I/O,
4644      * or
4645      * - regardless of whether bfqq is weight-raised, bfqq has
4646      *   however a long think time, during which it can absorb the
4647      *   effect of an appropriate number of extra I/O requests
4648      *   from other queues (see bfq_update_inject_limit for
4649      *   details on the computation of this number);
4650      * then injection can be performed without restrictions.
4651      */
4652     bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4653         !bfq_bfqq_has_short_ttime(in_serv_bfqq);
4654 
4655     /*
4656      * If
4657      * - the baseline total service time could not be sampled yet,
4658      *   so the inject limit happens to be still 0, and
4659      * - a lot of time has elapsed since the plugging of I/O
4660      *   dispatching started, so drive speed is being wasted
4661      *   significantly;
4662      * then temporarily raise inject limit to one request.
4663      */
4664     if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4665         bfq_bfqq_wait_request(in_serv_bfqq) &&
4666         time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4667                       bfqd->bfq_slice_idle)
4668         )
4669         limit = 1;
4670 
4671     if (bfqd->rq_in_driver >= limit)
4672         return NULL;
4673 
4674     /*
4675      * Linear search of the source queue for injection; but, with
4676      * a high probability, very few steps are needed to find a
4677      * candidate queue, i.e., a queue with enough budget left for
4678      * its next request. In fact:
4679      * - BFQ dynamically updates the budget of every queue so as
4680      *   to accommodate the expected backlog of the queue;
4681      * - if a queue gets all its requests dispatched as injected
4682      *   service, then the queue is removed from the active list
4683      *   (and re-added only if it gets new requests, but then it
4684      *   is assigned again enough budget for its new backlog).
4685      */
4686     list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
4687         if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4688             (in_serv_always_inject || bfqq->wr_coeff > 1) &&
4689             bfq_serv_to_charge(bfqq->next_rq, bfqq) <=
4690             bfq_bfqq_budget_left(bfqq)) {
4691             /*
4692              * Allow for only one large in-flight request
4693              * on non-rotational devices, for the
4694              * following reason. On non-rotationl drives,
4695              * large requests take much longer than
4696              * smaller requests to be served. In addition,
4697              * the drive prefers to serve large requests
4698              * w.r.t. to small ones, if it can choose. So,
4699              * having more than one large requests queued
4700              * in the drive may easily make the next first
4701              * request of the in-service queue wait for so
4702              * long to break bfqq's service guarantees. On
4703              * the bright side, large requests let the
4704              * drive reach a very high throughput, even if
4705              * there is only one in-flight large request
4706              * at a time.
4707              */
4708             if (blk_queue_nonrot(bfqd->queue) &&
4709                 blk_rq_sectors(bfqq->next_rq) >=
4710                 BFQQ_SECT_THR_NONROT)
4711                 limit = min_t(unsigned int, 1, limit);
4712             else
4713                 limit = in_serv_bfqq->inject_limit;
4714 
4715             if (bfqd->rq_in_driver < limit) {
4716                 bfqd->rqs_injected = true;
4717                 return bfqq;
4718             }
4719         }
4720 
4721     return NULL;
4722 }
4723 
4724 /*
4725  * Select a queue for service.  If we have a current queue in service,
4726  * check whether to continue servicing it, or retrieve and set a new one.
4727  */
4728 static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4729 {
4730     struct bfq_queue *bfqq;
4731     struct request *next_rq;
4732     enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4733 
4734     bfqq = bfqd->in_service_queue;
4735     if (!bfqq)
4736         goto new_queue;
4737 
4738     bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4739 
4740     /*
4741      * Do not expire bfqq for budget timeout if bfqq may be about
4742      * to enjoy device idling. The reason why, in this case, we
4743      * prevent bfqq from expiring is the same as in the comments
4744      * on the case where bfq_bfqq_must_idle() returns true, in
4745      * bfq_completed_request().
4746      */
4747     if (bfq_may_expire_for_budg_timeout(bfqq) &&
4748         !bfq_bfqq_must_idle(bfqq))
4749         goto expire;
4750 
4751 check_queue:
4752     /*
4753      * This loop is rarely executed more than once. Even when it
4754      * happens, it is much more convenient to re-execute this loop
4755      * than to return NULL and trigger a new dispatch to get a
4756      * request served.
4757      */
4758     next_rq = bfqq->next_rq;
4759     /*
4760      * If bfqq has requests queued and it has enough budget left to
4761      * serve them, keep the queue, otherwise expire it.
4762      */
4763     if (next_rq) {
4764         if (bfq_serv_to_charge(next_rq, bfqq) >
4765             bfq_bfqq_budget_left(bfqq)) {
4766             /*
4767              * Expire the queue for budget exhaustion,
4768              * which makes sure that the next budget is
4769              * enough to serve the next request, even if
4770              * it comes from the fifo expired path.
4771              */
4772             reason = BFQQE_BUDGET_EXHAUSTED;
4773             goto expire;
4774         } else {
4775             /*
4776              * The idle timer may be pending because we may
4777              * not disable disk idling even when a new request
4778              * arrives.
4779              */
4780             if (bfq_bfqq_wait_request(bfqq)) {
4781                 /*
4782                  * If we get here: 1) at least a new request
4783                  * has arrived but we have not disabled the
4784                  * timer because the request was too small,
4785                  * 2) then the block layer has unplugged
4786                  * the device, causing the dispatch to be
4787                  * invoked.
4788                  *
4789                  * Since the device is unplugged, now the
4790                  * requests are probably large enough to
4791                  * provide a reasonable throughput.
4792                  * So we disable idling.
4793                  */
4794                 bfq_clear_bfqq_wait_request(bfqq);
4795                 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4796             }
4797             goto keep_queue;
4798         }
4799     }
4800 
4801     /*
4802      * No requests pending. However, if the in-service queue is idling
4803      * for a new request, or has requests waiting for a completion and
4804      * may idle after their completion, then keep it anyway.
4805      *
4806      * Yet, inject service from other queues if it boosts
4807      * throughput and is possible.
4808      */
4809     if (bfq_bfqq_wait_request(bfqq) ||
4810         (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4811         struct bfq_queue *async_bfqq =
4812             bfqq->bic && bfqq->bic->bfqq[0] &&
4813             bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
4814             bfqq->bic->bfqq[0]->next_rq ?
4815             bfqq->bic->bfqq[0] : NULL;
4816         struct bfq_queue *blocked_bfqq =
4817             !hlist_empty(&bfqq->woken_list) ?
4818             container_of(bfqq->woken_list.first,
4819                      struct bfq_queue,
4820                      woken_list_node)
4821             : NULL;
4822 
4823         /*
4824          * The next four mutually-exclusive ifs decide
4825          * whether to try injection, and choose the queue to
4826          * pick an I/O request from.
4827          *
4828          * The first if checks whether the process associated
4829          * with bfqq has also async I/O pending. If so, it
4830          * injects such I/O unconditionally. Injecting async
4831          * I/O from the same process can cause no harm to the
4832          * process. On the contrary, it can only increase
4833          * bandwidth and reduce latency for the process.
4834          *
4835          * The second if checks whether there happens to be a
4836          * non-empty waker queue for bfqq, i.e., a queue whose
4837          * I/O needs to be completed for bfqq to receive new
4838          * I/O. This happens, e.g., if bfqq is associated with
4839          * a process that does some sync. A sync generates
4840          * extra blocking I/O, which must be completed before
4841          * the process associated with bfqq can go on with its
4842          * I/O. If the I/O of the waker queue is not served,
4843          * then bfqq remains empty, and no I/O is dispatched,
4844          * until the idle timeout fires for bfqq. This is
4845          * likely to result in lower bandwidth and higher
4846          * latencies for bfqq, and in a severe loss of total
4847          * throughput. The best action to take is therefore to
4848          * serve the waker queue as soon as possible. So do it
4849          * (without relying on the third alternative below for
4850          * eventually serving waker_bfqq's I/O; see the last
4851          * paragraph for further details). This systematic
4852          * injection of I/O from the waker queue does not
4853          * cause any delay to bfqq's I/O. On the contrary,
4854          * next bfqq's I/O is brought forward dramatically,
4855          * for it is not blocked for milliseconds.
4856          *
4857          * The third if checks whether there is a queue woken
4858          * by bfqq, and currently with pending I/O. Such a
4859          * woken queue does not steal bandwidth from bfqq,
4860          * because it remains soon without I/O if bfqq is not
4861          * served. So there is virtually no risk of loss of
4862          * bandwidth for bfqq if this woken queue has I/O
4863          * dispatched while bfqq is waiting for new I/O.
4864          *
4865          * The fourth if checks whether bfqq is a queue for
4866          * which it is better to avoid injection. It is so if
4867          * bfqq delivers more throughput when served without
4868          * any further I/O from other queues in the middle, or
4869          * if the service times of bfqq's I/O requests both
4870          * count more than overall throughput, and may be
4871          * easily increased by injection (this happens if bfqq
4872          * has a short think time). If none of these
4873          * conditions holds, then a candidate queue for
4874          * injection is looked for through
4875          * bfq_choose_bfqq_for_injection(). Note that the
4876          * latter may return NULL (for example if the inject
4877          * limit for bfqq is currently 0).
4878          *
4879          * NOTE: motivation for the second alternative
4880          *
4881          * Thanks to the way the inject limit is updated in
4882          * bfq_update_has_short_ttime(), it is rather likely
4883          * that, if I/O is being plugged for bfqq and the
4884          * waker queue has pending I/O requests that are
4885          * blocking bfqq's I/O, then the fourth alternative
4886          * above lets the waker queue get served before the
4887          * I/O-plugging timeout fires. So one may deem the
4888          * second alternative superfluous. It is not, because
4889          * the fourth alternative may be way less effective in
4890          * case of a synchronization. For two main
4891          * reasons. First, throughput may be low because the
4892          * inject limit may be too low to guarantee the same
4893          * amount of injected I/O, from the waker queue or
4894          * other queues, that the second alternative
4895          * guarantees (the second alternative unconditionally
4896          * injects a pending I/O request of the waker queue
4897          * for each bfq_dispatch_request()). Second, with the
4898          * fourth alternative, the duration of the plugging,
4899          * i.e., the time before bfqq finally receives new I/O,
4900          * may not be minimized, because the waker queue may
4901          * happen to be served only after other queues.
4902          */
4903         if (async_bfqq &&
4904             icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4905             bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
4906             bfq_bfqq_budget_left(async_bfqq))
4907             bfqq = bfqq->bic->bfqq[0];
4908         else if (bfqq->waker_bfqq &&
4909                bfq_bfqq_busy(bfqq->waker_bfqq) &&
4910                bfqq->waker_bfqq->next_rq &&
4911                bfq_serv_to_charge(bfqq->waker_bfqq->next_rq,
4912                           bfqq->waker_bfqq) <=
4913                bfq_bfqq_budget_left(bfqq->waker_bfqq)
4914             )
4915             bfqq = bfqq->waker_bfqq;
4916         else if (blocked_bfqq &&
4917                bfq_bfqq_busy(blocked_bfqq) &&
4918                blocked_bfqq->next_rq &&
4919                bfq_serv_to_charge(blocked_bfqq->next_rq,
4920                           blocked_bfqq) <=
4921                bfq_bfqq_budget_left(blocked_bfqq)
4922             )
4923             bfqq = blocked_bfqq;
4924         else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
4925              (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
4926               !bfq_bfqq_has_short_ttime(bfqq)))
4927             bfqq = bfq_choose_bfqq_for_injection(bfqd);
4928         else
4929             bfqq = NULL;
4930 
4931         goto keep_queue;
4932     }
4933 
4934     reason = BFQQE_NO_MORE_REQUESTS;
4935 expire:
4936     bfq_bfqq_expire(bfqd, bfqq, false, reason);
4937 new_queue:
4938     bfqq = bfq_set_in_service_queue(bfqd);
4939     if (bfqq) {
4940         bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
4941         goto check_queue;
4942     }
4943 keep_queue:
4944     if (bfqq)
4945         bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
4946     else
4947         bfq_log(bfqd, "select_queue: no queue returned");
4948 
4949     return bfqq;
4950 }
4951 
4952 static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4953 {
4954     struct bfq_entity *entity = &bfqq->entity;
4955 
4956     if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
4957         bfq_log_bfqq(bfqd, bfqq,
4958             "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
4959             jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
4960             jiffies_to_msecs(bfqq->wr_cur_max_time),
4961             bfqq->wr_coeff,
4962             bfqq->entity.weight, bfqq->entity.orig_weight);
4963 
4964         if (entity->prio_changed)
4965             bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
4966 
4967         /*
4968          * If the queue was activated in a burst, or too much
4969          * time has elapsed from the beginning of this
4970          * weight-raising period, then end weight raising.
4971          */
4972         if (bfq_bfqq_in_large_burst(bfqq))
4973             bfq_bfqq_end_wr(bfqq);
4974         else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
4975                         bfqq->wr_cur_max_time)) {
4976             if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
4977             time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
4978                            bfq_wr_duration(bfqd))) {
4979                 /*
4980                  * Either in interactive weight
4981                  * raising, or in soft_rt weight
4982                  * raising with the
4983                  * interactive-weight-raising period
4984                  * elapsed (so no switch back to
4985                  * interactive weight raising).
4986                  */
4987                 bfq_bfqq_end_wr(bfqq);
4988             } else { /*
4989                   * soft_rt finishing while still in
4990                   * interactive period, switch back to
4991                   * interactive weight raising
4992                   */
4993                 switch_back_to_interactive_wr(bfqq, bfqd);
4994                 bfqq->entity.prio_changed = 1;
4995             }
4996         }
4997         if (bfqq->wr_coeff > 1 &&
4998             bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
4999             bfqq->service_from_wr > max_service_from_wr) {
5000             /* see comments on max_service_from_wr */
5001             bfq_bfqq_end_wr(bfqq);
5002         }
5003     }
5004     /*
5005      * To improve latency (for this or other queues), immediately
5006      * update weight both if it must be raised and if it must be
5007      * lowered. Since, entity may be on some active tree here, and
5008      * might have a pending change of its ioprio class, invoke
5009      * next function with the last parameter unset (see the
5010      * comments on the function).
5011      */
5012     if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
5013         __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
5014                         entity, false);
5015 }
5016 
5017 /*
5018  * Dispatch next request from bfqq.
5019  */
5020 static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
5021                          struct bfq_queue *bfqq)
5022 {
5023     struct request *rq = bfqq->next_rq;
5024     unsigned long service_to_charge;
5025 
5026     service_to_charge = bfq_serv_to_charge(rq, bfqq);
5027 
5028     bfq_bfqq_served(bfqq, service_to_charge);
5029 
5030     if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
5031         bfqd->wait_dispatch = false;
5032         bfqd->waited_rq = rq;
5033     }
5034 
5035     bfq_dispatch_remove(bfqd->queue, rq);
5036 
5037     if (bfqq != bfqd->in_service_queue)
5038         goto return_rq;
5039 
5040     /*
5041      * If weight raising has to terminate for bfqq, then next
5042      * function causes an immediate update of bfqq's weight,
5043      * without waiting for next activation. As a consequence, on
5044      * expiration, bfqq will be timestamped as if has never been
5045      * weight-raised during this service slot, even if it has
5046      * received part or even most of the service as a
5047      * weight-raised queue. This inflates bfqq's timestamps, which
5048      * is beneficial, as bfqq is then more willing to leave the
5049      * device immediately to possible other weight-raised queues.
5050      */
5051     bfq_update_wr_data(bfqd, bfqq);
5052 
5053     /*
5054      * Expire bfqq, pretending that its budget expired, if bfqq
5055      * belongs to CLASS_IDLE and other queues are waiting for
5056      * service.
5057      */
5058     if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
5059         goto return_rq;
5060 
5061     bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
5062 
5063 return_rq:
5064     return rq;
5065 }
5066 
5067 static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
5068 {
5069     struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5070 
5071     /*
5072      * Avoiding lock: a race on bfqd->queued should cause at
5073      * most a call to dispatch for nothing
5074      */
5075     return !list_empty_careful(&bfqd->dispatch) ||
5076         READ_ONCE(bfqd->queued);
5077 }
5078 
5079 static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5080 {
5081     struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5082     struct request *rq = NULL;
5083     struct bfq_queue *bfqq = NULL;
5084 
5085     if (!list_empty(&bfqd->dispatch)) {
5086         rq = list_first_entry(&bfqd->dispatch, struct request,
5087                       queuelist);
5088         list_del_init(&rq->queuelist);
5089 
5090         bfqq = RQ_BFQQ(rq);
5091 
5092         if (bfqq) {
5093             /*
5094              * Increment counters here, because this
5095              * dispatch does not follow the standard
5096              * dispatch flow (where counters are
5097              * incremented)
5098              */
5099             bfqq->dispatched++;
5100 
5101             goto inc_in_driver_start_rq;
5102         }
5103 
5104         /*
5105          * We exploit the bfq_finish_requeue_request hook to
5106          * decrement rq_in_driver, but
5107          * bfq_finish_requeue_request will not be invoked on
5108          * this request. So, to avoid unbalance, just start
5109          * this request, without incrementing rq_in_driver. As
5110          * a negative consequence, rq_in_driver is deceptively
5111          * lower than it should be while this request is in
5112          * service. This may cause bfq_schedule_dispatch to be
5113          * invoked uselessly.
5114          *
5115          * As for implementing an exact solution, the
5116          * bfq_finish_requeue_request hook, if defined, is
5117          * probably invoked also on this request. So, by
5118          * exploiting this hook, we could 1) increment
5119          * rq_in_driver here, and 2) decrement it in
5120          * bfq_finish_requeue_request. Such a solution would
5121          * let the value of the counter be always accurate,
5122          * but it would entail using an extra interface
5123          * function. This cost seems higher than the benefit,
5124          * being the frequency of non-elevator-private
5125          * requests very low.
5126          */
5127         goto start_rq;
5128     }
5129 
5130     bfq_log(bfqd, "dispatch requests: %d busy queues",
5131         bfq_tot_busy_queues(bfqd));
5132 
5133     if (bfq_tot_busy_queues(bfqd) == 0)
5134         goto exit;
5135 
5136     /*
5137      * Force device to serve one request at a time if
5138      * strict_guarantees is true. Forcing this service scheme is
5139      * currently the ONLY way to guarantee that the request
5140      * service order enforced by the scheduler is respected by a
5141      * queueing device. Otherwise the device is free even to make
5142      * some unlucky request wait for as long as the device
5143      * wishes.
5144      *
5145      * Of course, serving one request at a time may cause loss of
5146      * throughput.
5147      */
5148     if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
5149         goto exit;
5150 
5151     bfqq = bfq_select_queue(bfqd);
5152     if (!bfqq)
5153         goto exit;
5154 
5155     rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
5156 
5157     if (rq) {
5158 inc_in_driver_start_rq:
5159         bfqd->rq_in_driver++;
5160 start_rq:
5161         rq->rq_flags |= RQF_STARTED;
5162     }
5163 exit:
5164     return rq;
5165 }
5166 
5167 #ifdef CONFIG_BFQ_CGROUP_DEBUG
5168 static void bfq_update_dispatch_stats(struct request_queue *q,
5169                       struct request *rq,
5170                       struct bfq_queue *in_serv_queue,
5171                       bool idle_timer_disabled)
5172 {
5173     struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
5174 
5175     if (!idle_timer_disabled && !bfqq)
5176         return;
5177 
5178     /*
5179      * rq and bfqq are guaranteed to exist until this function
5180      * ends, for the following reasons. First, rq can be
5181      * dispatched to the device, and then can be completed and
5182      * freed, only after this function ends. Second, rq cannot be
5183      * merged (and thus freed because of a merge) any longer,
5184      * because it has already started. Thus rq cannot be freed
5185      * before this function ends, and, since rq has a reference to
5186      * bfqq, the same guarantee holds for bfqq too.
5187      *
5188      * In addition, the following queue lock guarantees that
5189      * bfqq_group(bfqq) exists as well.
5190      */
5191     spin_lock_irq(&q->queue_lock);
5192     if (idle_timer_disabled)
5193         /*
5194          * Since the idle timer has been disabled,
5195          * in_serv_queue contained some request when
5196          * __bfq_dispatch_request was invoked above, which
5197          * implies that rq was picked exactly from
5198          * in_serv_queue. Thus in_serv_queue == bfqq, and is
5199          * therefore guaranteed to exist because of the above
5200          * arguments.
5201          */
5202         bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
5203     if (bfqq) {
5204         struct bfq_group *bfqg = bfqq_group(bfqq);
5205 
5206         bfqg_stats_update_avg_queue_size(bfqg);
5207         bfqg_stats_set_start_empty_time(bfqg);
5208         bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
5209     }
5210     spin_unlock_irq(&q->queue_lock);
5211 }
5212 #else
5213 static inline void bfq_update_dispatch_stats(struct request_queue *q,
5214                          struct request *rq,
5215                          struct bfq_queue *in_serv_queue,
5216                          bool idle_timer_disabled) {}
5217 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
5218 
5219 static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5220 {
5221     struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5222     struct request *rq;
5223     struct bfq_queue *in_serv_queue;
5224     bool waiting_rq, idle_timer_disabled = false;
5225 
5226     spin_lock_irq(&bfqd->lock);
5227 
5228     in_serv_queue = bfqd->in_service_queue;
5229     waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
5230 
5231     rq = __bfq_dispatch_request(hctx);
5232     if (in_serv_queue == bfqd->in_service_queue) {
5233         idle_timer_disabled =
5234             waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
5235     }
5236 
5237     spin_unlock_irq(&bfqd->lock);
5238     bfq_update_dispatch_stats(hctx->queue, rq,
5239             idle_timer_disabled ? in_serv_queue : NULL,
5240                 idle_timer_disabled);
5241 
5242     return rq;
5243 }
5244 
5245 /*
5246  * Task holds one reference to the queue, dropped when task exits.  Each rq
5247  * in-flight on this queue also holds a reference, dropped when rq is freed.
5248  *
5249  * Scheduler lock must be held here. Recall not to use bfqq after calling
5250  * this function on it.
5251  */
5252 void bfq_put_queue(struct bfq_queue *bfqq)
5253 {
5254     struct bfq_queue *item;
5255     struct hlist_node *n;
5256     struct bfq_group *bfqg = bfqq_group(bfqq);
5257 
5258     if (bfqq->bfqd)
5259         bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
5260                  bfqq, bfqq->ref);
5261 
5262     bfqq->ref--;
5263     if (bfqq->ref)
5264         return;
5265 
5266     if (!hlist_unhashed(&bfqq->burst_list_node)) {
5267         hlist_del_init(&bfqq->burst_list_node);
5268         /*
5269          * Decrement also burst size after the removal, if the
5270          * process associated with bfqq is exiting, and thus
5271          * does not contribute to the burst any longer. This
5272          * decrement helps filter out false positives of large
5273          * bursts, when some short-lived process (often due to
5274          * the execution of commands by some service) happens
5275          * to start and exit while a complex application is
5276          * starting, and thus spawning several processes that
5277          * do I/O (and that *must not* be treated as a large
5278          * burst, see comments on bfq_handle_burst).
5279          *
5280          * In particular, the decrement is performed only if:
5281          * 1) bfqq is not a merged queue, because, if it is,
5282          * then this free of bfqq is not triggered by the exit
5283          * of the process bfqq is associated with, but exactly
5284          * by the fact that bfqq has just been merged.
5285          * 2) burst_size is greater than 0, to handle
5286          * unbalanced decrements. Unbalanced decrements may
5287          * happen in te following case: bfqq is inserted into
5288          * the current burst list--without incrementing
5289          * bust_size--because of a split, but the current
5290          * burst list is not the burst list bfqq belonged to
5291          * (see comments on the case of a split in
5292          * bfq_set_request).
5293          */
5294         if (bfqq->bic && bfqq->bfqd->burst_size > 0)
5295             bfqq->bfqd->burst_size--;
5296     }
5297 
5298     /*
5299      * bfqq does not exist any longer, so it cannot be woken by
5300      * any other queue, and cannot wake any other queue. Then bfqq
5301      * must be removed from the woken list of its possible waker
5302      * queue, and all queues in the woken list of bfqq must stop
5303      * having a waker queue. Strictly speaking, these updates
5304      * should be performed when bfqq remains with no I/O source
5305      * attached to it, which happens before bfqq gets freed. In
5306      * particular, this happens when the last process associated
5307      * with bfqq exits or gets associated with a different
5308      * queue. However, both events lead to bfqq being freed soon,
5309      * and dangling references would come out only after bfqq gets
5310      * freed. So these updates are done here, as a simple and safe
5311      * way to handle all cases.
5312      */
5313     /* remove bfqq from woken list */
5314     if (!hlist_unhashed(&bfqq->woken_list_node))
5315         hlist_del_init(&bfqq->woken_list_node);
5316 
5317     /* reset waker for all queues in woken list */
5318     hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
5319                   woken_list_node) {
5320         item->waker_bfqq = NULL;
5321         hlist_del_init(&item->woken_list_node);
5322     }
5323 
5324     if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)
5325         bfqq->bfqd->last_completed_rq_bfqq = NULL;
5326 
5327     kmem_cache_free(bfq_pool, bfqq);
5328     bfqg_and_blkg_put(bfqg);
5329 }
5330 
5331 static void bfq_put_stable_ref(struct bfq_queue *bfqq)
5332 {
5333     bfqq->stable_ref--;
5334     bfq_put_queue(bfqq);
5335 }
5336 
5337 void bfq_put_cooperator(struct bfq_queue *bfqq)
5338 {
5339     struct bfq_queue *__bfqq, *next;
5340 
5341     /*
5342      * If this queue was scheduled to merge with another queue, be
5343      * sure to drop the reference taken on that queue (and others in
5344      * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
5345      */
5346     __bfqq = bfqq->new_bfqq;
5347     while (__bfqq) {
5348         if (__bfqq == bfqq)
5349             break;
5350         next = __bfqq->new_bfqq;
5351         bfq_put_queue(__bfqq);
5352         __bfqq = next;
5353     }
5354 }
5355 
5356 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
5357 {
5358     if (bfqq == bfqd->in_service_queue) {
5359         __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
5360         bfq_schedule_dispatch(bfqd);
5361     }
5362 
5363     bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
5364 
5365     bfq_put_cooperator(bfqq);
5366 
5367     bfq_release_process_ref(bfqd, bfqq);
5368 }
5369 
5370 static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
5371 {
5372     struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
5373     struct bfq_data *bfqd;
5374 
5375     if (bfqq)
5376         bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
5377 
5378     if (bfqq && bfqd) {
5379         unsigned long flags;
5380 
5381         spin_lock_irqsave(&bfqd->lock, flags);
5382         bfqq->bic = NULL;
5383         bfq_exit_bfqq(bfqd, bfqq);
5384         bic_set_bfqq(bic, NULL, is_sync);
5385         spin_unlock_irqrestore(&bfqd->lock, flags);
5386     }
5387 }
5388 
5389 static void bfq_exit_icq(struct io_cq *icq)
5390 {
5391     struct bfq_io_cq *bic = icq_to_bic(icq);
5392 
5393     if (bic->stable_merge_bfqq) {
5394         struct bfq_data *bfqd = bic->stable_merge_bfqq->bfqd;
5395 
5396         /*
5397          * bfqd is NULL if scheduler already exited, and in
5398          * that case this is the last time bfqq is accessed.
5399          */
5400         if (bfqd) {
5401             unsigned long flags;
5402 
5403             spin_lock_irqsave(&bfqd->lock, flags);
5404             bfq_put_stable_ref(bic->stable_merge_bfqq);
5405             spin_unlock_irqrestore(&bfqd->lock, flags);
5406         } else {
5407             bfq_put_stable_ref(bic->stable_merge_bfqq);
5408         }
5409     }
5410 
5411     bfq_exit_icq_bfqq(bic, true);
5412     bfq_exit_icq_bfqq(bic, false);
5413 }
5414 
5415 /*
5416  * Update the entity prio values; note that the new values will not
5417  * be used until the next (re)activation.
5418  */
5419 static void
5420 bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
5421 {
5422     struct task_struct *tsk = current;
5423     int ioprio_class;
5424     struct bfq_data *bfqd = bfqq->bfqd;
5425 
5426     if (!bfqd)
5427         return;
5428 
5429     ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5430     switch (ioprio_class) {
5431     default:
5432         pr_err("bdi %s: bfq: bad prio class %d\n",
5433             bdi_dev_name(bfqq->bfqd->queue->disk->bdi),
5434             ioprio_class);
5435         fallthrough;
5436     case IOPRIO_CLASS_NONE:
5437         /*
5438          * No prio set, inherit CPU scheduling settings.
5439          */
5440         bfqq->new_ioprio = task_nice_ioprio(tsk);
5441         bfqq->new_ioprio_class = task_nice_ioclass(tsk);
5442         break;
5443     case IOPRIO_CLASS_RT:
5444         bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5445         bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
5446         break;
5447     case IOPRIO_CLASS_BE:
5448         bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5449         bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
5450         break;
5451     case IOPRIO_CLASS_IDLE:
5452         bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5453         bfqq->new_ioprio = 7;
5454         break;
5455     }
5456 
5457     if (bfqq->new_ioprio >= IOPRIO_NR_LEVELS) {
5458         pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5459             bfqq->new_ioprio);
5460         bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
5461     }
5462 
5463     bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
5464     bfq_log_bfqq(bfqd, bfqq, "new_ioprio %d new_weight %d",
5465              bfqq->new_ioprio, bfqq->entity.new_weight);
5466     bfqq->entity.prio_changed = 1;
5467 }
5468 
5469 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5470                        struct bio *bio, bool is_sync,
5471                        struct bfq_io_cq *bic,
5472                        bool respawn);
5473 
5474 static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5475 {
5476     struct bfq_data *bfqd = bic_to_bfqd(bic);
5477     struct bfq_queue *bfqq;
5478     int ioprio = bic->icq.ioc->ioprio;
5479 
5480     /*
5481      * This condition may trigger on a newly created bic, be sure to
5482      * drop the lock before returning.
5483      */
5484     if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5485         return;
5486 
5487     bic->ioprio = ioprio;
5488 
5489     bfqq = bic_to_bfqq(bic, false);
5490     if (bfqq) {
5491         bfq_release_process_ref(bfqd, bfqq);
5492         bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
5493         bic_set_bfqq(bic, bfqq, false);
5494     }
5495 
5496     bfqq = bic_to_bfqq(bic, true);
5497     if (bfqq)
5498         bfq_set_next_ioprio_data(bfqq, bic);
5499 }
5500 
5501 static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5502               struct bfq_io_cq *bic, pid_t pid, int is_sync)
5503 {
5504     u64 now_ns = ktime_get_ns();
5505 
5506     RB_CLEAR_NODE(&bfqq->entity.rb_node);
5507     INIT_LIST_HEAD(&bfqq->fifo);
5508     INIT_HLIST_NODE(&bfqq->burst_list_node);
5509     INIT_HLIST_NODE(&bfqq->woken_list_node);
5510     INIT_HLIST_HEAD(&bfqq->woken_list);
5511 
5512     bfqq->ref = 0;
5513     bfqq->bfqd = bfqd;
5514 
5515     if (bic)
5516         bfq_set_next_ioprio_data(bfqq, bic);
5517 
5518     if (is_sync) {
5519         /*
5520          * No need to mark as has_short_ttime if in
5521          * idle_class, because no device idling is performed
5522          * for queues in idle class
5523          */
5524         if (!bfq_class_idle(bfqq))
5525             /* tentatively mark as has_short_ttime */
5526             bfq_mark_bfqq_has_short_ttime(bfqq);
5527         bfq_mark_bfqq_sync(bfqq);
5528         bfq_mark_bfqq_just_created(bfqq);
5529     } else
5530         bfq_clear_bfqq_sync(bfqq);
5531 
5532     /* set end request to minus infinity from now */
5533     bfqq->ttime.last_end_request = now_ns + 1;
5534 
5535     bfqq->creation_time = jiffies;
5536 
5537     bfqq->io_start_time = now_ns;
5538 
5539     bfq_mark_bfqq_IO_bound(bfqq);
5540 
5541     bfqq->pid = pid;
5542 
5543     /* Tentative initial value to trade off between thr and lat */
5544     bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5545     bfqq->budget_timeout = bfq_smallest_from_now();
5546 
5547     bfqq->wr_coeff = 1;
5548     bfqq->last_wr_start_finish = jiffies;
5549     bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5550     bfqq->split_time = bfq_smallest_from_now();
5551 
5552     /*
5553      * To not forget the possibly high bandwidth consumed by a
5554      * process/queue in the recent past,
5555      * bfq_bfqq_softrt_next_start() returns a value at least equal
5556      * to the current value of bfqq->soft_rt_next_start (see
5557      * comments on bfq_bfqq_softrt_next_start).  Set
5558      * soft_rt_next_start to now, to mean that bfqq has consumed
5559      * no bandwidth so far.
5560      */
5561     bfqq->soft_rt_next_start = jiffies;
5562 
5563     /* first request is almost certainly seeky */
5564     bfqq->seek_history = 1;
5565 }
5566 
5567 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5568                            struct bfq_group *bfqg,
5569                            int ioprio_class, int ioprio)
5570 {
5571     switch (ioprio_class) {
5572     case IOPRIO_CLASS_RT:
5573         return &bfqg->async_bfqq[0][ioprio];
5574     case IOPRIO_CLASS_NONE:
5575         ioprio = IOPRIO_BE_NORM;
5576         fallthrough;
5577     case IOPRIO_CLASS_BE:
5578         return &bfqg->async_bfqq[1][ioprio];
5579     case IOPRIO_CLASS_IDLE:
5580         return &bfqg->async_idle_bfqq;
5581     default:
5582         return NULL;
5583     }
5584 }
5585 
5586 static struct bfq_queue *
5587 bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5588               struct bfq_io_cq *bic,
5589               struct bfq_queue *last_bfqq_created)
5590 {
5591     struct bfq_queue *new_bfqq =
5592         bfq_setup_merge(bfqq, last_bfqq_created);
5593 
5594     if (!new_bfqq)
5595         return bfqq;
5596 
5597     if (new_bfqq->bic)
5598         new_bfqq->bic->stably_merged = true;
5599     bic->stably_merged = true;
5600 
5601     /*
5602      * Reusing merge functions. This implies that
5603      * bfqq->bic must be set too, for
5604      * bfq_merge_bfqqs to correctly save bfqq's
5605      * state before killing it.
5606      */
5607     bfqq->bic = bic;
5608     bfq_merge_bfqqs(bfqd, bic, bfqq, new_bfqq);
5609 
5610     return new_bfqq;
5611 }
5612 
5613 /*
5614  * Many throughput-sensitive workloads are made of several parallel
5615  * I/O flows, with all flows generated by the same application, or
5616  * more generically by the same task (e.g., system boot). The most
5617  * counterproductive action with these workloads is plugging I/O
5618  * dispatch when one of the bfq_queues associated with these flows
5619  * remains temporarily empty.
5620  *
5621  * To avoid this plugging, BFQ has been using a burst-handling
5622  * mechanism for years now. This mechanism has proven effective for
5623  * throughput, and not detrimental for service guarantees. The
5624  * following function pushes this mechanism a little bit further,
5625  * basing on the following two facts.
5626  *
5627  * First, all the I/O flows of a the same application or task
5628  * contribute to the execution/completion of that common application
5629  * or task. So the performance figures that matter are total
5630  * throughput of the flows and task-wide I/O latency.  In particular,
5631  * these flows do not need to be protected from each other, in terms
5632  * of individual bandwidth or latency.
5633  *
5634  * Second, the above fact holds regardless of the number of flows.
5635  *
5636  * Putting these two facts together, this commits merges stably the
5637  * bfq_queues associated with these I/O flows, i.e., with the
5638  * processes that generate these IO/ flows, regardless of how many the
5639  * involved processes are.
5640  *
5641  * To decide whether a set of bfq_queues is actually associated with
5642  * the I/O flows of a common application or task, and to merge these
5643  * queues stably, this function operates as follows: given a bfq_queue,
5644  * say Q2, currently being created, and the last bfq_queue, say Q1,
5645  * created before Q2, Q2 is merged stably with Q1 if
5646  * - very little time has elapsed since when Q1 was created
5647  * - Q2 has the same ioprio as Q1
5648  * - Q2 belongs to the same group as Q1
5649  *
5650  * Merging bfq_queues also reduces scheduling overhead. A fio test
5651  * with ten random readers on /dev/nullb shows a throughput boost of
5652  * 40%, with a quadcore. Since BFQ's execution time amounts to ~50% of
5653  * the total per-request processing time, the above throughput boost
5654  * implies that BFQ's overhead is reduced by more than 50%.
5655  *
5656  * This new mechanism most certainly obsoletes the current
5657  * burst-handling heuristics. We keep those heuristics for the moment.
5658  */
5659 static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
5660                               struct bfq_queue *bfqq,
5661                               struct bfq_io_cq *bic)
5662 {
5663     struct bfq_queue **source_bfqq = bfqq->entity.parent ?
5664         &bfqq->entity.parent->last_bfqq_created :
5665         &bfqd->last_bfqq_created;
5666 
5667     struct bfq_queue *last_bfqq_created = *source_bfqq;
5668 
5669     /*
5670      * If last_bfqq_created has not been set yet, then init it. If
5671      * it has been set already, but too long ago, then move it
5672      * forward to bfqq. Finally, move also if bfqq belongs to a
5673      * different group than last_bfqq_created, or if bfqq has a
5674      * different ioprio or ioprio_class. If none of these
5675      * conditions holds true, then try an early stable merge or
5676      * schedule a delayed stable merge.
5677      *
5678      * A delayed merge is scheduled (instead of performing an
5679      * early merge), in case bfqq might soon prove to be more
5680      * throughput-beneficial if not merged. Currently this is
5681      * possible only if bfqd is rotational with no queueing. For
5682      * such a drive, not merging bfqq is better for throughput if
5683      * bfqq happens to contain sequential I/O. So, we wait a
5684      * little bit for enough I/O to flow through bfqq. After that,
5685      * if such an I/O is sequential, then the merge is
5686      * canceled. Otherwise the merge is finally performed.
5687      */
5688     if (!last_bfqq_created ||
5689         time_before(last_bfqq_created->creation_time +
5690             msecs_to_jiffies(bfq_activation_stable_merging),
5691             bfqq->creation_time) ||
5692         bfqq->entity.parent != last_bfqq_created->entity.parent ||
5693         bfqq->ioprio != last_bfqq_created->ioprio ||
5694         bfqq->ioprio_class != last_bfqq_created->ioprio_class)
5695         *source_bfqq = bfqq;
5696     else if (time_after_eq(last_bfqq_created->creation_time +
5697                  bfqd->bfq_burst_interval,
5698                  bfqq->creation_time)) {
5699         if (likely(bfqd->nonrot_with_queueing))
5700             /*
5701              * With this type of drive, leaving
5702              * bfqq alone may provide no
5703              * throughput benefits compared with
5704              * merging bfqq. So merge bfqq now.
5705              */
5706             bfqq = bfq_do_early_stable_merge(bfqd, bfqq,
5707                              bic,
5708                              last_bfqq_created);
5709         else { /* schedule tentative stable merge */
5710             /*
5711              * get reference on last_bfqq_created,
5712              * to prevent it from being freed,
5713              * until we decide whether to merge
5714              */
5715             last_bfqq_created->ref++;
5716             /*
5717              * need to keep track of stable refs, to
5718              * compute process refs correctly
5719              */
5720             last_bfqq_created->stable_ref++;
5721             /*
5722              * Record the bfqq to merge to.
5723              */
5724             bic->stable_merge_bfqq = last_bfqq_created;
5725         }
5726     }
5727 
5728     return bfqq;
5729 }
5730 
5731 
5732 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5733                        struct bio *bio, bool is_sync,
5734                        struct bfq_io_cq *bic,
5735                        bool respawn)
5736 {
5737     const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5738     const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5739     struct bfq_queue **async_bfqq = NULL;
5740     struct bfq_queue *bfqq;
5741     struct bfq_group *bfqg;
5742 
5743     bfqg = bfq_bio_bfqg(bfqd, bio);
5744     if (!is_sync) {
5745         async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5746                           ioprio);
5747         bfqq = *async_bfqq;
5748         if (bfqq)
5749             goto out;
5750     }
5751 
5752     bfqq = kmem_cache_alloc_node(bfq_pool,
5753                      GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5754                      bfqd->queue->node);
5755 
5756     if (bfqq) {
5757         bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5758                   is_sync);
5759         bfq_init_entity(&bfqq->entity, bfqg);
5760         bfq_log_bfqq(bfqd, bfqq, "allocated");
5761     } else {
5762         bfqq = &bfqd->oom_bfqq;
5763         bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5764         goto out;
5765     }
5766 
5767     /*
5768      * Pin the queue now that it's allocated, scheduler exit will
5769      * prune it.
5770      */
5771     if (async_bfqq) {
5772         bfqq->ref++; /*
5773                   * Extra group reference, w.r.t. sync
5774                   * queue. This extra reference is removed
5775                   * only if bfqq->bfqg disappears, to
5776                   * guarantee that this queue is not freed
5777                   * until its group goes away.
5778                   */
5779         bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5780                  bfqq, bfqq->ref);
5781         *async_bfqq = bfqq;
5782     }
5783 
5784 out:
5785     bfqq->ref++; /* get a process reference to this queue */
5786 
5787     if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn)
5788         bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic);
5789     return bfqq;
5790 }
5791 
5792 static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5793                     struct bfq_queue *bfqq)
5794 {
5795     struct bfq_ttime *ttime = &bfqq->ttime;
5796     u64 elapsed;
5797 
5798     /*
5799      * We are really interested in how long it takes for the queue to
5800      * become busy when there is no outstanding IO for this queue. So
5801      * ignore cases when the bfq queue has already IO queued.
5802      */
5803     if (bfqq->dispatched || bfq_bfqq_busy(bfqq))
5804         return;
5805     elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
5806     elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5807 
5808     ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
5809     ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed,  8);
5810     ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5811                      ttime->ttime_samples);
5812 }
5813 
5814 static void
5815 bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5816                struct request *rq)
5817 {
5818     bfqq->seek_history <<= 1;
5819     bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5820 
5821     if (bfqq->wr_coeff > 1 &&
5822         bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5823         BFQQ_TOTALLY_SEEKY(bfqq)) {
5824         if (time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
5825                        bfq_wr_duration(bfqd))) {
5826             /*
5827              * In soft_rt weight raising with the
5828              * interactive-weight-raising period
5829              * elapsed (so no switch back to
5830              * interactive weight raising).
5831              */
5832             bfq_bfqq_end_wr(bfqq);
5833         } else { /*
5834               * stopping soft_rt weight raising
5835               * while still in interactive period,
5836               * switch back to interactive weight
5837               * raising
5838               */
5839             switch_back_to_interactive_wr(bfqq, bfqd);
5840             bfqq->entity.prio_changed = 1;
5841         }
5842     }
5843 }
5844 
5845 static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5846                        struct bfq_queue *bfqq,
5847                        struct bfq_io_cq *bic)
5848 {
5849     bool has_short_ttime = true, state_changed;
5850 
5851     /*
5852      * No need to update has_short_ttime if bfqq is async or in
5853      * idle io prio class, or if bfq_slice_idle is zero, because
5854      * no device idling is performed for bfqq in this case.
5855      */
5856     if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5857         bfqd->bfq_slice_idle == 0)
5858         return;
5859 
5860     /* Idle window just restored, statistics are meaningless. */
5861     if (time_is_after_eq_jiffies(bfqq->split_time +
5862                      bfqd->bfq_wr_min_idle_time))
5863         return;
5864 
5865     /* Think time is infinite if no process is linked to
5866      * bfqq. Otherwise check average think time to decide whether
5867      * to mark as has_short_ttime. To this goal, compare average
5868      * think time with half the I/O-plugging timeout.
5869      */
5870     if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
5871         (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5872          bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle>>1))
5873         has_short_ttime = false;
5874 
5875     state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5876 
5877     if (has_short_ttime)
5878         bfq_mark_bfqq_has_short_ttime(bfqq);
5879     else
5880         bfq_clear_bfqq_has_short_ttime(bfqq);
5881 
5882     /*
5883      * Until the base value for the total service time gets
5884      * finally computed for bfqq, the inject limit does depend on
5885      * the think-time state (short|long). In particular, the limit
5886      * is 0 or 1 if the think time is deemed, respectively, as
5887      * short or long (details in the comments in
5888      * bfq_update_inject_limit()). Accordingly, the next
5889      * instructions reset the inject limit if the think-time state
5890      * has changed and the above base value is still to be
5891      * computed.
5892      *
5893      * However, the reset is performed only if more than 100 ms
5894      * have elapsed since the last update of the inject limit, or
5895      * (inclusive) if the change is from short to long think
5896      * time. The reason for this waiting is as follows.
5897      *
5898      * bfqq may have a long think time because of a
5899      * synchronization with some other queue, i.e., because the
5900      * I/O of some other queue may need to be completed for bfqq
5901      * to receive new I/O. Details in the comments on the choice
5902      * of the queue for injection in bfq_select_queue().
5903      *
5904      * As stressed in those comments, if such a synchronization is
5905      * actually in place, then, without injection on bfqq, the
5906      * blocking I/O cannot happen to served while bfqq is in
5907      * service. As a consequence, if bfqq is granted
5908      * I/O-dispatch-plugging, then bfqq remains empty, and no I/O
5909      * is dispatched, until the idle timeout fires. This is likely
5910      * to result in lower bandwidth and higher latencies for bfqq,
5911      * and in a severe loss of total throughput.
5912      *
5913      * On the opposite end, a non-zero inject limit may allow the
5914      * I/O that blocks bfqq to be executed soon, and therefore
5915      * bfqq to receive new I/O soon.
5916      *
5917      * But, if the blocking gets actually eliminated, then the
5918      * next think-time sample for bfqq may be very low. This in
5919      * turn may cause bfqq's think time to be deemed
5920      * short. Without the 100 ms barrier, this new state change
5921      * would cause the body of the next if to be executed
5922      * immediately. But this would set to 0 the inject
5923      * limit. Without injection, the blocking I/O would cause the
5924      * think time of bfqq to become long again, and therefore the
5925      * inject limit to be raised again, and so on. The only effect
5926      * of such a steady oscillation between the two think-time
5927      * states would be to prevent effective injection on bfqq.
5928      *
5929      * In contrast, if the inject limit is not reset during such a
5930      * long time interval as 100 ms, then the number of short
5931      * think time samples can grow significantly before the reset
5932      * is performed. As a consequence, the think time state can
5933      * become stable before the reset. Therefore there will be no
5934      * state change when the 100 ms elapse, and no reset of the
5935      * inject limit. The inject limit remains steadily equal to 1
5936      * both during and after the 100 ms. So injection can be
5937      * performed at all times, and throughput gets boosted.
5938      *
5939      * An inject limit equal to 1 is however in conflict, in
5940      * general, with the fact that the think time of bfqq is
5941      * short, because injection may be likely to delay bfqq's I/O
5942      * (as explained in the comments in
5943      * bfq_update_inject_limit()). But this does not happen in
5944      * this special case, because bfqq's low think time is due to
5945      * an effective handling of a synchronization, through
5946      * injection. In this special case, bfqq's I/O does not get
5947      * delayed by injection; on the contrary, bfqq's I/O is
5948      * brought forward, because it is not blocked for
5949      * milliseconds.
5950      *
5951      * In addition, serving the blocking I/O much sooner, and much
5952      * more frequently than once per I/O-plugging timeout, makes
5953      * it much quicker to detect a waker queue (the concept of
5954      * waker queue is defined in the comments in
5955      * bfq_add_request()). This makes it possible to start sooner
5956      * to boost throughput more effectively, by injecting the I/O
5957      * of the waker queue unconditionally on every
5958      * bfq_dispatch_request().
5959      *
5960      * One last, important benefit of not resetting the inject
5961      * limit before 100 ms is that, during this time interval, the
5962      * base value for the total service time is likely to get
5963      * finally computed for bfqq, freeing the inject limit from
5964      * its relation with the think time.
5965      */
5966     if (state_changed && bfqq->last_serv_time_ns == 0 &&
5967         (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
5968                       msecs_to_jiffies(100)) ||
5969          !has_short_ttime))
5970         bfq_reset_inject_limit(bfqd, bfqq);
5971 }
5972 
5973 /*
5974  * Called when a new fs request (rq) is added to bfqq.  Check if there's
5975  * something we should do about it.
5976  */
5977 static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5978                 struct request *rq)
5979 {
5980     if (rq->cmd_flags & REQ_META)
5981         bfqq->meta_pending++;
5982 
5983     bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
5984 
5985     if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
5986         bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
5987                  blk_rq_sectors(rq) < 32;
5988         bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
5989 
5990         /*
5991          * There is just this request queued: if
5992          * - the request is small, and
5993          * - we are idling to boost throughput, and
5994          * - the queue is not to be expired,
5995          * then just exit.
5996          *
5997          * In this way, if the device is being idled to wait
5998          * for a new request from the in-service queue, we
5999          * avoid unplugging the device and committing the
6000          * device to serve just a small request. In contrast
6001          * we wait for the block layer to decide when to
6002          * unplug the device: hopefully, new requests will be
6003          * merged to this one quickly, then the device will be
6004          * unplugged and larger requests will be dispatched.
6005          */
6006         if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
6007             !budget_timeout)
6008             return;
6009 
6010         /*
6011          * A large enough request arrived, or idling is being
6012          * performed to preserve service guarantees, or
6013          * finally the queue is to be expired: in all these
6014          * cases disk idling is to be stopped, so clear
6015          * wait_request flag and reset timer.
6016          */
6017         bfq_clear_bfqq_wait_request(bfqq);
6018         hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
6019 
6020         /*
6021          * The queue is not empty, because a new request just
6022          * arrived. Hence we can safely expire the queue, in
6023          * case of budget timeout, without risking that the
6024          * timestamps of the queue are not updated correctly.
6025          * See [1] for more details.
6026          */
6027         if (budget_timeout)
6028             bfq_bfqq_expire(bfqd, bfqq, false,
6029                     BFQQE_BUDGET_TIMEOUT);
6030     }
6031 }
6032 
6033 static void bfqq_request_allocated(struct bfq_queue *bfqq)
6034 {
6035     struct bfq_entity *entity = &bfqq->entity;
6036 
6037     for_each_entity(entity)
6038         entity->allocated++;
6039 }
6040 
6041 static void bfqq_request_freed(struct bfq_queue *bfqq)
6042 {
6043     struct bfq_entity *entity = &bfqq->entity;
6044 
6045     for_each_entity(entity)
6046         entity->allocated--;
6047 }
6048 
6049 /* returns true if it causes the idle timer to be disabled */
6050 static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
6051 {
6052     struct bfq_queue *bfqq = RQ_BFQQ(rq),
6053         *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true,
6054                          RQ_BIC(rq));
6055     bool waiting, idle_timer_disabled = false;
6056 
6057     if (new_bfqq) {
6058         /*
6059          * Release the request's reference to the old bfqq
6060          * and make sure one is taken to the shared queue.
6061          */
6062         bfqq_request_allocated(new_bfqq);
6063         bfqq_request_freed(bfqq);
6064         new_bfqq->ref++;
6065         /*
6066          * If the bic associated with the process
6067          * issuing this request still points to bfqq
6068          * (and thus has not been already redirected
6069          * to new_bfqq or even some other bfq_queue),
6070          * then complete the merge and redirect it to
6071          * new_bfqq.
6072          */
6073         if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
6074             bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
6075                     bfqq, new_bfqq);
6076 
6077         bfq_clear_bfqq_just_created(bfqq);
6078         /*
6079          * rq is about to be enqueued into new_bfqq,
6080          * release rq reference on bfqq
6081          */
6082         bfq_put_queue(bfqq);
6083         rq->elv.priv[1] = new_bfqq;
6084         bfqq = new_bfqq;
6085     }
6086 
6087     bfq_update_io_thinktime(bfqd, bfqq);
6088     bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
6089     bfq_update_io_seektime(bfqd, bfqq, rq);
6090 
6091     waiting = bfqq && bfq_bfqq_wait_request(bfqq);
6092     bfq_add_request(rq);
6093     idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
6094 
6095     rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
6096     list_add_tail(&rq->queuelist, &bfqq->fifo);
6097 
6098     bfq_rq_enqueued(bfqd, bfqq, rq);
6099 
6100     return idle_timer_disabled;
6101 }
6102 
6103 #ifdef CONFIG_BFQ_CGROUP_DEBUG
6104 static void bfq_update_insert_stats(struct request_queue *q,
6105                     struct bfq_queue *bfqq,
6106                     bool idle_timer_disabled,
6107                     blk_opf_t cmd_flags)
6108 {
6109     if (!bfqq)
6110         return;
6111 
6112     /*
6113      * bfqq still exists, because it can disappear only after
6114      * either it is merged with another queue, or the process it
6115      * is associated with exits. But both actions must be taken by
6116      * the same process currently executing this flow of
6117      * instructions.
6118      *
6119      * In addition, the following queue lock guarantees that
6120      * bfqq_group(bfqq) exists as well.
6121      */
6122     spin_lock_irq(&q->queue_lock);
6123     bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
6124     if (idle_timer_disabled)
6125         bfqg_stats_update_idle_time(bfqq_group(bfqq));
6126     spin_unlock_irq(&q->queue_lock);
6127 }
6128 #else
6129 static inline void bfq_update_insert_stats(struct request_queue *q,
6130                        struct bfq_queue *bfqq,
6131                        bool idle_timer_disabled,
6132                        blk_opf_t cmd_flags) {}
6133 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
6134 
6135 static struct bfq_queue *bfq_init_rq(struct request *rq);
6136 
6137 static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
6138                    bool at_head)
6139 {
6140     struct request_queue *q = hctx->queue;
6141     struct bfq_data *bfqd = q->elevator->elevator_data;
6142     struct bfq_queue *bfqq;
6143     bool idle_timer_disabled = false;
6144     blk_opf_t cmd_flags;
6145     LIST_HEAD(free);
6146 
6147 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6148     if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
6149         bfqg_stats_update_legacy_io(q, rq);
6150 #endif
6151     spin_lock_irq(&bfqd->lock);
6152     bfqq = bfq_init_rq(rq);
6153     if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
6154         spin_unlock_irq(&bfqd->lock);
6155         blk_mq_free_requests(&free);
6156         return;
6157     }
6158 
6159     trace_block_rq_insert(rq);
6160 
6161     if (!bfqq || at_head) {
6162         if (at_head)
6163             list_add(&rq->queuelist, &bfqd->dispatch);
6164         else
6165             list_add_tail(&rq->queuelist, &bfqd->dispatch);
6166     } else {
6167         idle_timer_disabled = __bfq_insert_request(bfqd, rq);
6168         /*
6169          * Update bfqq, because, if a queue merge has occurred
6170          * in __bfq_insert_request, then rq has been
6171          * redirected into a new queue.
6172          */
6173         bfqq = RQ_BFQQ(rq);
6174 
6175         if (rq_mergeable(rq)) {
6176             elv_rqhash_add(q, rq);
6177             if (!q->last_merge)
6178                 q->last_merge = rq;
6179         }
6180     }
6181 
6182     /*
6183      * Cache cmd_flags before releasing scheduler lock, because rq
6184      * may disappear afterwards (for example, because of a request
6185      * merge).
6186      */
6187     cmd_flags = rq->cmd_flags;
6188     spin_unlock_irq(&bfqd->lock);
6189 
6190     bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
6191                 cmd_flags);
6192 }
6193 
6194 static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
6195                 struct list_head *list, bool at_head)
6196 {
6197     while (!list_empty(list)) {
6198         struct request *rq;
6199 
6200         rq = list_first_entry(list, struct request, queuelist);
6201         list_del_init(&rq->queuelist);
6202         bfq_insert_request(hctx, rq, at_head);
6203     }
6204 }
6205 
6206 static void bfq_update_hw_tag(struct bfq_data *bfqd)
6207 {
6208     struct bfq_queue *bfqq = bfqd->in_service_queue;
6209 
6210     bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
6211                        bfqd->rq_in_driver);
6212 
6213     if (bfqd->hw_tag == 1)
6214         return;
6215 
6216     /*
6217      * This sample is valid if the number of outstanding requests
6218      * is large enough to allow a queueing behavior.  Note that the
6219      * sum is not exact, as it's not taking into account deactivated
6220      * requests.
6221      */
6222     if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
6223         return;
6224 
6225     /*
6226      * If active queue hasn't enough requests and can idle, bfq might not
6227      * dispatch sufficient requests to hardware. Don't zero hw_tag in this
6228      * case
6229      */
6230     if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
6231         bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
6232         BFQ_HW_QUEUE_THRESHOLD &&
6233         bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
6234         return;
6235 
6236     if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
6237         return;
6238 
6239     bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
6240     bfqd->max_rq_in_driver = 0;
6241     bfqd->hw_tag_samples = 0;
6242 
6243     bfqd->nonrot_with_queueing =
6244         blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
6245 }
6246 
6247 static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
6248 {
6249     u64 now_ns;
6250     u32 delta_us;
6251 
6252     bfq_update_hw_tag(bfqd);
6253 
6254     bfqd->rq_in_driver--;
6255     bfqq->dispatched--;
6256 
6257     if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
6258         /*
6259          * Set budget_timeout (which we overload to store the
6260          * time at which the queue remains with no backlog and
6261          * no outstanding request; used by the weight-raising
6262          * mechanism).
6263          */
6264         bfqq->budget_timeout = jiffies;
6265 
6266         bfq_weights_tree_remove(bfqd, bfqq);
6267     }
6268 
6269     now_ns = ktime_get_ns();
6270 
6271     bfqq->ttime.last_end_request = now_ns;
6272 
6273     /*
6274      * Using us instead of ns, to get a reasonable precision in
6275      * computing rate in next check.
6276      */
6277     delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
6278 
6279     /*
6280      * If the request took rather long to complete, and, according
6281      * to the maximum request size recorded, this completion latency
6282      * implies that the request was certainly served at a very low
6283      * rate (less than 1M sectors/sec), then the whole observation
6284      * interval that lasts up to this time instant cannot be a
6285      * valid time interval for computing a new peak rate.  Invoke
6286      * bfq_update_rate_reset to have the following three steps
6287      * taken:
6288      * - close the observation interval at the last (previous)
6289      *   request dispatch or completion
6290      * - compute rate, if possible, for that observation interval
6291      * - reset to zero samples, which will trigger a proper
6292      *   re-initialization of the observation interval on next
6293      *   dispatch
6294      */
6295     if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
6296        (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
6297             1UL<<(BFQ_RATE_SHIFT - 10))
6298         bfq_update_rate_reset(bfqd, NULL);
6299     bfqd->last_completion = now_ns;
6300     /*
6301      * Shared queues are likely to receive I/O at a high
6302      * rate. This may deceptively let them be considered as wakers
6303      * of other queues. But a false waker will unjustly steal
6304      * bandwidth to its supposedly woken queue. So considering
6305      * also shared queues in the waking mechanism may cause more
6306      * control troubles than throughput benefits. Then reset
6307      * last_completed_rq_bfqq if bfqq is a shared queue.
6308      */
6309     if (!bfq_bfqq_coop(bfqq))
6310         bfqd->last_completed_rq_bfqq = bfqq;
6311     else
6312         bfqd->last_completed_rq_bfqq = NULL;
6313 
6314     /*
6315      * If we are waiting to discover whether the request pattern
6316      * of the task associated with the queue is actually
6317      * isochronous, and both requisites for this condition to hold
6318      * are now satisfied, then compute soft_rt_next_start (see the
6319      * comments on the function bfq_bfqq_softrt_next_start()). We
6320      * do not compute soft_rt_next_start if bfqq is in interactive
6321      * weight raising (see the comments in bfq_bfqq_expire() for
6322      * an explanation). We schedule this delayed update when bfqq
6323      * expires, if it still has in-flight requests.
6324      */
6325     if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
6326         RB_EMPTY_ROOT(&bfqq->sort_list) &&
6327         bfqq->wr_coeff != bfqd->bfq_wr_coeff)
6328         bfqq->soft_rt_next_start =
6329             bfq_bfqq_softrt_next_start(bfqd, bfqq);
6330 
6331     /*
6332      * If this is the in-service queue, check if it needs to be expired,
6333      * or if we want to idle in case it has no pending requests.
6334      */
6335     if (bfqd->in_service_queue == bfqq) {
6336         if (bfq_bfqq_must_idle(bfqq)) {
6337             if (bfqq->dispatched == 0)
6338                 bfq_arm_slice_timer(bfqd);
6339             /*
6340              * If we get here, we do not expire bfqq, even
6341              * if bfqq was in budget timeout or had no
6342              * more requests (as controlled in the next
6343              * conditional instructions). The reason for
6344              * not expiring bfqq is as follows.
6345              *
6346              * Here bfqq->dispatched > 0 holds, but
6347              * bfq_bfqq_must_idle() returned true. This
6348              * implies that, even if no request arrives
6349              * for bfqq before bfqq->dispatched reaches 0,
6350              * bfqq will, however, not be expired on the
6351              * completion event that causes bfqq->dispatch
6352              * to reach zero. In contrast, on this event,
6353              * bfqq will start enjoying device idling
6354              * (I/O-dispatch plugging).
6355              *
6356              * But, if we expired bfqq here, bfqq would
6357              * not have the chance to enjoy device idling
6358              * when bfqq->dispatched finally reaches
6359              * zero. This would expose bfqq to violation
6360              * of its reserved service guarantees.
6361              */
6362             return;
6363         } else if (bfq_may_expire_for_budg_timeout(bfqq))
6364             bfq_bfqq_expire(bfqd, bfqq, false,
6365                     BFQQE_BUDGET_TIMEOUT);
6366         else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
6367              (bfqq->dispatched == 0 ||
6368               !bfq_better_to_idle(bfqq)))
6369             bfq_bfqq_expire(bfqd, bfqq, false,
6370                     BFQQE_NO_MORE_REQUESTS);
6371     }
6372 
6373     if (!bfqd->rq_in_driver)
6374         bfq_schedule_dispatch(bfqd);
6375 }
6376 
6377 /*
6378  * The processes associated with bfqq may happen to generate their
6379  * cumulative I/O at a lower rate than the rate at which the device
6380  * could serve the same I/O. This is rather probable, e.g., if only
6381  * one process is associated with bfqq and the device is an SSD. It
6382  * results in bfqq becoming often empty while in service. In this
6383  * respect, if BFQ is allowed to switch to another queue when bfqq
6384  * remains empty, then the device goes on being fed with I/O requests,
6385  * and the throughput is not affected. In contrast, if BFQ is not
6386  * allowed to switch to another queue---because bfqq is sync and
6387  * I/O-dispatch needs to be plugged while bfqq is temporarily
6388  * empty---then, during the service of bfqq, there will be frequent
6389  * "service holes", i.e., time intervals during which bfqq gets empty
6390  * and the device can only consume the I/O already queued in its
6391  * hardware queues. During service holes, the device may even get to
6392  * remaining idle. In the end, during the service of bfqq, the device
6393  * is driven at a lower speed than the one it can reach with the kind
6394  * of I/O flowing through bfqq.
6395  *
6396  * To counter this loss of throughput, BFQ implements a "request
6397  * injection mechanism", which tries to fill the above service holes
6398  * with I/O requests taken from other queues. The hard part in this
6399  * mechanism is finding the right amount of I/O to inject, so as to
6400  * both boost throughput and not break bfqq's bandwidth and latency
6401  * guarantees. In this respect, the mechanism maintains a per-queue
6402  * inject limit, computed as below. While bfqq is empty, the injection
6403  * mechanism dispatches extra I/O requests only until the total number
6404  * of I/O requests in flight---i.e., already dispatched but not yet
6405  * completed---remains lower than this limit.
6406  *
6407  * A first definition comes in handy to introduce the algorithm by
6408  * which the inject limit is computed.  We define as first request for
6409  * bfqq, an I/O request for bfqq that arrives while bfqq is in
6410  * service, and causes bfqq to switch from empty to non-empty. The
6411  * algorithm updates the limit as a function of the effect of
6412  * injection on the service times of only the first requests of
6413  * bfqq. The reason for this restriction is that these are the
6414  * requests whose service time is affected most, because they are the
6415  * first to arrive after injection possibly occurred.
6416  *
6417  * To evaluate the effect of injection, the algorithm measures the
6418  * "total service time" of first requests. We define as total service
6419  * time of an I/O request, the time that elapses since when the
6420  * request is enqueued into bfqq, to when it is completed. This
6421  * quantity allows the whole effect of injection to be measured. It is
6422  * easy to see why. Suppose that some requests of other queues are
6423  * actually injected while bfqq is empty, and that a new request R
6424  * then arrives for bfqq. If the device does start to serve all or
6425  * part of the injected requests during the service hole, then,
6426  * because of this extra service, it may delay the next invocation of
6427  * the dispatch hook of BFQ. Then, even after R gets eventually
6428  * dispatched, the device may delay the actual service of R if it is
6429  * still busy serving the extra requests, or if it decides to serve,
6430  * before R, some extra request still present in its queues. As a
6431  * conclusion, the cumulative extra delay caused by injection can be
6432  * easily evaluated by just comparing the total service time of first
6433  * requests with and without injection.
6434  *
6435  * The limit-update algorithm works as follows. On the arrival of a
6436  * first request of bfqq, the algorithm measures the total time of the
6437  * request only if one of the three cases below holds, and, for each
6438  * case, it updates the limit as described below:
6439  *
6440  * (1) If there is no in-flight request. This gives a baseline for the
6441  *     total service time of the requests of bfqq. If the baseline has
6442  *     not been computed yet, then, after computing it, the limit is
6443  *     set to 1, to start boosting throughput, and to prepare the
6444  *     ground for the next case. If the baseline has already been
6445  *     computed, then it is updated, in case it results to be lower
6446  *     than the previous value.
6447  *
6448  * (2) If the limit is higher than 0 and there are in-flight
6449  *     requests. By comparing the total service time in this case with
6450  *     the above baseline, it is possible to know at which extent the
6451  *     current value of the limit is inflating the total service
6452  *     time. If the inflation is below a certain threshold, then bfqq
6453  *     is assumed to be suffering from no perceivable loss of its
6454  *     service guarantees, and the limit is even tentatively
6455  *     increased. If the inflation is above the threshold, then the
6456  *     limit is decreased. Due to the lack of any hysteresis, this
6457  *     logic makes the limit oscillate even in steady workload
6458  *     conditions. Yet we opted for it, because it is fast in reaching
6459  *     the best value for the limit, as a function of the current I/O
6460  *     workload. To reduce oscillations, this step is disabled for a
6461  *     short time interval after the limit happens to be decreased.
6462  *
6463  * (3) Periodically, after resetting the limit, to make sure that the
6464  *     limit eventually drops in case the workload changes. This is
6465  *     needed because, after the limit has gone safely up for a
6466  *     certain workload, it is impossible to guess whether the
6467  *     baseline total service time may have changed, without measuring
6468  *     it again without injection. A more effective version of this
6469  *     step might be to just sample the baseline, by interrupting
6470  *     injection only once, and then to reset/lower the limit only if
6471  *     the total service time with the current limit does happen to be
6472  *     too large.
6473  *
6474  * More details on each step are provided in the comments on the
6475  * pieces of code that implement these steps: the branch handling the
6476  * transition from empty to non empty in bfq_add_request(), the branch
6477  * handling injection in bfq_select_queue(), and the function
6478  * bfq_choose_bfqq_for_injection(). These comments also explain some
6479  * exceptions, made by the injection mechanism in some special cases.
6480  */
6481 static void bfq_update_inject_limit(struct bfq_data *bfqd,
6482                     struct bfq_queue *bfqq)
6483 {
6484     u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns;
6485     unsigned int old_limit = bfqq->inject_limit;
6486 
6487     if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
6488         u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
6489 
6490         if (tot_time_ns >= threshold && old_limit > 0) {
6491             bfqq->inject_limit--;
6492             bfqq->decrease_time_jif = jiffies;
6493         } else if (tot_time_ns < threshold &&
6494                old_limit <= bfqd->max_rq_in_driver)
6495             bfqq->inject_limit++;
6496     }
6497 
6498     /*
6499      * Either we still have to compute the base value for the
6500      * total service time, and there seem to be the right
6501      * conditions to do it, or we can lower the last base value
6502      * computed.
6503      *
6504      * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
6505      * request in flight, because this function is in the code
6506      * path that handles the completion of a request of bfqq, and,
6507      * in particular, this function is executed before
6508      * bfqd->rq_in_driver is decremented in such a code path.
6509      */
6510     if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) ||
6511         tot_time_ns < bfqq->last_serv_time_ns) {
6512         if (bfqq->last_serv_time_ns == 0) {
6513             /*
6514              * Now we certainly have a base value: make sure we
6515              * start trying injection.
6516              */
6517             bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
6518         }
6519         bfqq->last_serv_time_ns = tot_time_ns;
6520     } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
6521         /*
6522          * No I/O injected and no request still in service in
6523          * the drive: these are the exact conditions for
6524          * computing the base value of the total service time
6525          * for bfqq. So let's update this value, because it is
6526          * rather variable. For example, it varies if the size
6527          * or the spatial locality of the I/O requests in bfqq
6528          * change.
6529          */
6530         bfqq->last_serv_time_ns = tot_time_ns;
6531 
6532 
6533     /* update complete, not waiting for any request completion any longer */
6534     bfqd->waited_rq = NULL;
6535     bfqd->rqs_injected = false;
6536 }
6537 
6538 /*
6539  * Handle either a requeue or a finish for rq. The things to do are
6540  * the same in both cases: all references to rq are to be dropped. In
6541  * particular, rq is considered completed from the point of view of
6542  * the scheduler.
6543  */
6544 static void bfq_finish_requeue_request(struct request *rq)
6545 {
6546     struct bfq_queue *bfqq = RQ_BFQQ(rq);
6547     struct bfq_data *bfqd;
6548     unsigned long flags;
6549 
6550     /*
6551      * rq either is not associated with any icq, or is an already
6552      * requeued request that has not (yet) been re-inserted into
6553      * a bfq_queue.
6554      */
6555     if (!rq->elv.icq || !bfqq)
6556         return;
6557 
6558     bfqd = bfqq->bfqd;
6559 
6560     if (rq->rq_flags & RQF_STARTED)
6561         bfqg_stats_update_completion(bfqq_group(bfqq),
6562                          rq->start_time_ns,
6563                          rq->io_start_time_ns,
6564                          rq->cmd_flags);
6565 
6566     spin_lock_irqsave(&bfqd->lock, flags);
6567     if (likely(rq->rq_flags & RQF_STARTED)) {
6568         if (rq == bfqd->waited_rq)
6569             bfq_update_inject_limit(bfqd, bfqq);
6570 
6571         bfq_completed_request(bfqq, bfqd);
6572     }
6573     bfqq_request_freed(bfqq);
6574     bfq_put_queue(bfqq);
6575     RQ_BIC(rq)->requests--;
6576     spin_unlock_irqrestore(&bfqd->lock, flags);
6577 
6578     /*
6579      * Reset private fields. In case of a requeue, this allows
6580      * this function to correctly do nothing if it is spuriously
6581      * invoked again on this same request (see the check at the
6582      * beginning of the function). Probably, a better general
6583      * design would be to prevent blk-mq from invoking the requeue
6584      * or finish hooks of an elevator, for a request that is not
6585      * referred by that elevator.
6586      *
6587      * Resetting the following fields would break the
6588      * request-insertion logic if rq is re-inserted into a bfq
6589      * internal queue, without a re-preparation. Here we assume
6590      * that re-insertions of requeued requests, without
6591      * re-preparation, can happen only for pass_through or at_head
6592      * requests (which are not re-inserted into bfq internal
6593      * queues).
6594      */
6595     rq->elv.priv[0] = NULL;
6596     rq->elv.priv[1] = NULL;
6597 }
6598 
6599 static void bfq_finish_request(struct request *rq)
6600 {
6601     bfq_finish_requeue_request(rq);
6602 
6603     if (rq->elv.icq) {
6604         put_io_context(rq->elv.icq->ioc);
6605         rq->elv.icq = NULL;
6606     }
6607 }
6608 
6609 /*
6610  * Removes the association between the current task and bfqq, assuming
6611  * that bic points to the bfq iocontext of the task.
6612  * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
6613  * was the last process referring to that bfqq.
6614  */
6615 static struct bfq_queue *
6616 bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
6617 {
6618     bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
6619 
6620     if (bfqq_process_refs(bfqq) == 1) {
6621         bfqq->pid = current->pid;
6622         bfq_clear_bfqq_coop(bfqq);
6623         bfq_clear_bfqq_split_coop(bfqq);
6624         return bfqq;
6625     }
6626 
6627     bic_set_bfqq(bic, NULL, 1);
6628 
6629     bfq_put_cooperator(bfqq);
6630 
6631     bfq_release_process_ref(bfqq->bfqd, bfqq);
6632     return NULL;
6633 }
6634 
6635 static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
6636                            struct bfq_io_cq *bic,
6637                            struct bio *bio,
6638                            bool split, bool is_sync,
6639                            bool *new_queue)
6640 {
6641     struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
6642 
6643     if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6644         return bfqq;
6645 
6646     if (new_queue)
6647         *new_queue = true;
6648 
6649     if (bfqq)
6650         bfq_put_queue(bfqq);
6651     bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, split);
6652 
6653     bic_set_bfqq(bic, bfqq, is_sync);
6654     if (split && is_sync) {
6655         if ((bic->was_in_burst_list && bfqd->large_burst) ||
6656             bic->saved_in_large_burst)
6657             bfq_mark_bfqq_in_large_burst(bfqq);
6658         else {
6659             bfq_clear_bfqq_in_large_burst(bfqq);
6660             if (bic->was_in_burst_list)
6661                 /*
6662                  * If bfqq was in the current
6663                  * burst list before being
6664                  * merged, then we have to add
6665                  * it back. And we do not need
6666                  * to increase burst_size, as
6667                  * we did not decrement
6668                  * burst_size when we removed
6669                  * bfqq from the burst list as
6670                  * a consequence of a merge
6671                  * (see comments in
6672                  * bfq_put_queue). In this
6673                  * respect, it would be rather
6674                  * costly to know whether the
6675                  * current burst list is still
6676                  * the same burst list from
6677                  * which bfqq was removed on
6678                  * the merge. To avoid this
6679                  * cost, if bfqq was in a
6680                  * burst list, then we add
6681                  * bfqq to the current burst
6682                  * list without any further
6683                  * check. This can cause
6684                  * inappropriate insertions,
6685                  * but rarely enough to not
6686                  * harm the detection of large
6687                  * bursts significantly.
6688                  */
6689                 hlist_add_head(&bfqq->burst_list_node,
6690                            &bfqd->burst_list);
6691         }
6692         bfqq->split_time = jiffies;
6693     }
6694 
6695     return bfqq;
6696 }
6697 
6698 /*
6699  * Only reset private fields. The actual request preparation will be
6700  * performed by bfq_init_rq, when rq is either inserted or merged. See
6701  * comments on bfq_init_rq for the reason behind this delayed
6702  * preparation.
6703  */
6704 static void bfq_prepare_request(struct request *rq)
6705 {
6706     rq->elv.icq = ioc_find_get_icq(rq->q);
6707 
6708     /*
6709      * Regardless of whether we have an icq attached, we have to
6710      * clear the scheduler pointers, as they might point to
6711      * previously allocated bic/bfqq structs.
6712      */
6713     rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6714 }
6715 
6716 /*
6717  * If needed, init rq, allocate bfq data structures associated with
6718  * rq, and increment reference counters in the destination bfq_queue
6719  * for rq. Return the destination bfq_queue for rq, or NULL is rq is
6720  * not associated with any bfq_queue.
6721  *
6722  * This function is invoked by the functions that perform rq insertion
6723  * or merging. One may have expected the above preparation operations
6724  * to be performed in bfq_prepare_request, and not delayed to when rq
6725  * is inserted or merged. The rationale behind this delayed
6726  * preparation is that, after the prepare_request hook is invoked for
6727  * rq, rq may still be transformed into a request with no icq, i.e., a
6728  * request not associated with any queue. No bfq hook is invoked to
6729  * signal this transformation. As a consequence, should these
6730  * preparation operations be performed when the prepare_request hook
6731  * is invoked, and should rq be transformed one moment later, bfq
6732  * would end up in an inconsistent state, because it would have
6733  * incremented some queue counters for an rq destined to
6734  * transformation, without any chance to correctly lower these
6735  * counters back. In contrast, no transformation can still happen for
6736  * rq after rq has been inserted or merged. So, it is safe to execute
6737  * these preparation operations when rq is finally inserted or merged.
6738  */
6739 static struct bfq_queue *bfq_init_rq(struct request *rq)
6740 {
6741     struct request_queue *q = rq->q;
6742     struct bio *bio = rq->bio;
6743     struct bfq_data *bfqd = q->elevator->elevator_data;
6744     struct bfq_io_cq *bic;
6745     const int is_sync = rq_is_sync(rq);
6746     struct bfq_queue *bfqq;
6747     bool new_queue = false;
6748     bool bfqq_already_existing = false, split = false;
6749 
6750     if (unlikely(!rq->elv.icq))
6751         return NULL;
6752 
6753     /*
6754      * Assuming that elv.priv[1] is set only if everything is set
6755      * for this rq. This holds true, because this function is
6756      * invoked only for insertion or merging, and, after such
6757      * events, a request cannot be manipulated any longer before
6758      * being removed from bfq.
6759      */
6760     if (rq->elv.priv[1])
6761         return rq->elv.priv[1];
6762 
6763     bic = icq_to_bic(rq->elv.icq);
6764 
6765     bfq_check_ioprio_change(bic, bio);
6766 
6767     bfq_bic_update_cgroup(bic, bio);
6768 
6769     bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
6770                      &new_queue);
6771 
6772     if (likely(!new_queue)) {
6773         /* If the queue was seeky for too long, break it apart. */
6774         if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
6775             !bic->stably_merged) {
6776             struct bfq_queue *old_bfqq = bfqq;
6777 
6778             /* Update bic before losing reference to bfqq */
6779             if (bfq_bfqq_in_large_burst(bfqq))
6780                 bic->saved_in_large_burst = true;
6781 
6782             bfqq = bfq_split_bfqq(bic, bfqq);
6783             split = true;
6784 
6785             if (!bfqq) {
6786                 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6787                                  true, is_sync,
6788                                  NULL);
6789                 bfqq->waker_bfqq = old_bfqq->waker_bfqq;
6790                 bfqq->tentative_waker_bfqq = NULL;
6791 
6792                 /*
6793                  * If the waker queue disappears, then
6794                  * new_bfqq->waker_bfqq must be
6795                  * reset. So insert new_bfqq into the
6796                  * woken_list of the waker. See
6797                  * bfq_check_waker for details.
6798                  */
6799                 if (bfqq->waker_bfqq)
6800                     hlist_add_head(&bfqq->woken_list_node,
6801                                &bfqq->waker_bfqq->woken_list);
6802             } else
6803                 bfqq_already_existing = true;
6804         }
6805     }
6806 
6807     bfqq_request_allocated(bfqq);
6808     bfqq->ref++;
6809     bic->requests++;
6810     bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6811              rq, bfqq, bfqq->ref);
6812 
6813     rq->elv.priv[0] = bic;
6814     rq->elv.priv[1] = bfqq;
6815 
6816     /*
6817      * If a bfq_queue has only one process reference, it is owned
6818      * by only this bic: we can then set bfqq->bic = bic. in
6819      * addition, if the queue has also just been split, we have to
6820      * resume its state.
6821      */
6822     if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6823         bfqq->bic = bic;
6824         if (split) {
6825             /*
6826              * The queue has just been split from a shared
6827              * queue: restore the idle window and the
6828              * possible weight raising period.
6829              */
6830             bfq_bfqq_resume_state(bfqq, bfqd, bic,
6831                           bfqq_already_existing);
6832         }
6833     }
6834 
6835     /*
6836      * Consider bfqq as possibly belonging to a burst of newly
6837      * created queues only if:
6838      * 1) A burst is actually happening (bfqd->burst_size > 0)
6839      * or
6840      * 2) There is no other active queue. In fact, if, in
6841      *    contrast, there are active queues not belonging to the
6842      *    possible burst bfqq may belong to, then there is no gain
6843      *    in considering bfqq as belonging to a burst, and
6844      *    therefore in not weight-raising bfqq. See comments on
6845      *    bfq_handle_burst().
6846      *
6847      * This filtering also helps eliminating false positives,
6848      * occurring when bfqq does not belong to an actual large
6849      * burst, but some background task (e.g., a service) happens
6850      * to trigger the creation of new queues very close to when
6851      * bfqq and its possible companion queues are created. See
6852      * comments on bfq_handle_burst() for further details also on
6853      * this issue.
6854      */
6855     if (unlikely(bfq_bfqq_just_created(bfqq) &&
6856              (bfqd->burst_size > 0 ||
6857               bfq_tot_busy_queues(bfqd) == 0)))
6858         bfq_handle_burst(bfqd, bfqq);
6859 
6860     return bfqq;
6861 }
6862 
6863 static void
6864 bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6865 {
6866     enum bfqq_expiration reason;
6867     unsigned long flags;
6868 
6869     spin_lock_irqsave(&bfqd->lock, flags);
6870 
6871     /*
6872      * Considering that bfqq may be in race, we should firstly check
6873      * whether bfqq is in service before doing something on it. If
6874      * the bfqq in race is not in service, it has already been expired
6875      * through __bfq_bfqq_expire func and its wait_request flags has
6876      * been cleared in __bfq_bfqd_reset_in_service func.
6877      */
6878     if (bfqq != bfqd->in_service_queue) {
6879         spin_unlock_irqrestore(&bfqd->lock, flags);
6880         return;
6881     }
6882 
6883     bfq_clear_bfqq_wait_request(bfqq);
6884 
6885     if (bfq_bfqq_budget_timeout(bfqq))
6886         /*
6887          * Also here the queue can be safely expired
6888          * for budget timeout without wasting
6889          * guarantees
6890          */
6891         reason = BFQQE_BUDGET_TIMEOUT;
6892     else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
6893         /*
6894          * The queue may not be empty upon timer expiration,
6895          * because we may not disable the timer when the
6896          * first request of the in-service queue arrives
6897          * during disk idling.
6898          */
6899         reason = BFQQE_TOO_IDLE;
6900     else
6901         goto schedule_dispatch;
6902 
6903     bfq_bfqq_expire(bfqd, bfqq, true, reason);
6904 
6905 schedule_dispatch:
6906     bfq_schedule_dispatch(bfqd);
6907     spin_unlock_irqrestore(&bfqd->lock, flags);
6908 }
6909 
6910 /*
6911  * Handler of the expiration of the timer running if the in-service queue
6912  * is idling inside its time slice.
6913  */
6914 static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
6915 {
6916     struct bfq_data *bfqd = container_of(timer, struct bfq_data,
6917                          idle_slice_timer);
6918     struct bfq_queue *bfqq = bfqd->in_service_queue;
6919 
6920     /*
6921      * Theoretical race here: the in-service queue can be NULL or
6922      * different from the queue that was idling if a new request
6923      * arrives for the current queue and there is a full dispatch
6924      * cycle that changes the in-service queue.  This can hardly
6925      * happen, but in the worst case we just expire a queue too
6926      * early.
6927      */
6928     if (bfqq)
6929         bfq_idle_slice_timer_body(bfqd, bfqq);
6930 
6931     return HRTIMER_NORESTART;
6932 }
6933 
6934 static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
6935                  struct bfq_queue **bfqq_ptr)
6936 {
6937     struct bfq_queue *bfqq = *bfqq_ptr;
6938 
6939     bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
6940     if (bfqq) {
6941         bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
6942 
6943         bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
6944                  bfqq, bfqq->ref);
6945         bfq_put_queue(bfqq);
6946         *bfqq_ptr = NULL;
6947     }
6948 }
6949 
6950 /*
6951  * Release all the bfqg references to its async queues.  If we are
6952  * deallocating the group these queues may still contain requests, so
6953  * we reparent them to the root cgroup (i.e., the only one that will
6954  * exist for sure until all the requests on a device are gone).
6955  */
6956 void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
6957 {
6958     int i, j;
6959 
6960     for (i = 0; i < 2; i++)
6961         for (j = 0; j < IOPRIO_NR_LEVELS; j++)
6962             __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
6963 
6964     __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
6965 }
6966 
6967 /*
6968  * See the comments on bfq_limit_depth for the purpose of
6969  * the depths set in the function. Return minimum shallow depth we'll use.
6970  */
6971 static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
6972 {
6973     unsigned int depth = 1U << bt->sb.shift;
6974 
6975     bfqd->full_depth_shift = bt->sb.shift;
6976     /*
6977      * In-word depths if no bfq_queue is being weight-raised:
6978      * leaving 25% of tags only for sync reads.
6979      *
6980      * In next formulas, right-shift the value
6981      * (1U<<bt->sb.shift), instead of computing directly
6982      * (1U<<(bt->sb.shift - something)), to be robust against
6983      * any possible value of bt->sb.shift, without having to
6984      * limit 'something'.
6985      */
6986     /* no more than 50% of tags for async I/O */
6987     bfqd->word_depths[0][0] = max(depth >> 1, 1U);
6988     /*
6989      * no more than 75% of tags for sync writes (25% extra tags
6990      * w.r.t. async I/O, to prevent async I/O from starving sync
6991      * writes)
6992      */
6993     bfqd->word_depths[0][1] = max((depth * 3) >> 2, 1U);
6994 
6995     /*
6996      * In-word depths in case some bfq_queue is being weight-
6997      * raised: leaving ~63% of tags for sync reads. This is the
6998      * highest percentage for which, in our tests, application
6999      * start-up times didn't suffer from any regression due to tag
7000      * shortage.
7001      */
7002     /* no more than ~18% of tags for async I/O */
7003     bfqd->word_depths[1][0] = max((depth * 3) >> 4, 1U);
7004     /* no more than ~37% of tags for sync writes (~20% extra tags) */
7005     bfqd->word_depths[1][1] = max((depth * 6) >> 4, 1U);
7006 }
7007 
7008 static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
7009 {
7010     struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
7011     struct blk_mq_tags *tags = hctx->sched_tags;
7012 
7013     bfq_update_depths(bfqd, &tags->bitmap_tags);
7014     sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, 1);
7015 }
7016 
7017 static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
7018 {
7019     bfq_depth_updated(hctx);
7020     return 0;
7021 }
7022 
7023 static void bfq_exit_queue(struct elevator_queue *e)
7024 {
7025     struct bfq_data *bfqd = e->elevator_data;
7026     struct bfq_queue *bfqq, *n;
7027 
7028     hrtimer_cancel(&bfqd->idle_slice_timer);
7029 
7030     spin_lock_irq(&bfqd->lock);
7031     list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
7032         bfq_deactivate_bfqq(bfqd, bfqq, false, false);
7033     spin_unlock_irq(&bfqd->lock);
7034 
7035     hrtimer_cancel(&bfqd->idle_slice_timer);
7036 
7037     /* release oom-queue reference to root group */
7038     bfqg_and_blkg_put(bfqd->root_group);
7039 
7040 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7041     blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
7042 #else
7043     spin_lock_irq(&bfqd->lock);
7044     bfq_put_async_queues(bfqd, bfqd->root_group);
7045     kfree(bfqd->root_group);
7046     spin_unlock_irq(&bfqd->lock);
7047 #endif
7048 
7049     blk_stat_disable_accounting(bfqd->queue);
7050     wbt_enable_default(bfqd->queue);
7051 
7052     kfree(bfqd);
7053 }
7054 
7055 static void bfq_init_root_group(struct bfq_group *root_group,
7056                 struct bfq_data *bfqd)
7057 {
7058     int i;
7059 
7060 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7061     root_group->entity.parent = NULL;
7062     root_group->my_entity = NULL;
7063     root_group->bfqd = bfqd;
7064 #endif
7065     root_group->rq_pos_tree = RB_ROOT;
7066     for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
7067         root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
7068     root_group->sched_data.bfq_class_idle_last_service = jiffies;
7069 }
7070 
7071 static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
7072 {
7073     struct bfq_data *bfqd;
7074     struct elevator_queue *eq;
7075 
7076     eq = elevator_alloc(q, e);
7077     if (!eq)
7078         return -ENOMEM;
7079 
7080     bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
7081     if (!bfqd) {
7082         kobject_put(&eq->kobj);
7083         return -ENOMEM;
7084     }
7085     eq->elevator_data = bfqd;
7086 
7087     spin_lock_irq(&q->queue_lock);
7088     q->elevator = eq;
7089     spin_unlock_irq(&q->queue_lock);
7090 
7091     /*
7092      * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
7093      * Grab a permanent reference to it, so that the normal code flow
7094      * will not attempt to free it.
7095      */
7096     bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
7097     bfqd->oom_bfqq.ref++;
7098     bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
7099     bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
7100     bfqd->oom_bfqq.entity.new_weight =
7101         bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
7102 
7103     /* oom_bfqq does not participate to bursts */
7104     bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
7105 
7106     /*
7107      * Trigger weight initialization, according to ioprio, at the
7108      * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
7109      * class won't be changed any more.
7110      */
7111     bfqd->oom_bfqq.entity.prio_changed = 1;
7112 
7113     bfqd->queue = q;
7114 
7115     INIT_LIST_HEAD(&bfqd->dispatch);
7116 
7117     hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
7118              HRTIMER_MODE_REL);
7119     bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
7120 
7121     bfqd->queue_weights_tree = RB_ROOT_CACHED;
7122     bfqd->num_groups_with_pending_reqs = 0;
7123 
7124     INIT_LIST_HEAD(&bfqd->active_list);
7125     INIT_LIST_HEAD(&bfqd->idle_list);
7126     INIT_HLIST_HEAD(&bfqd->burst_list);
7127 
7128     bfqd->hw_tag = -1;
7129     bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
7130 
7131     bfqd->bfq_max_budget = bfq_default_max_budget;
7132 
7133     bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
7134     bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
7135     bfqd->bfq_back_max = bfq_back_max;
7136     bfqd->bfq_back_penalty = bfq_back_penalty;
7137     bfqd->bfq_slice_idle = bfq_slice_idle;
7138     bfqd->bfq_timeout = bfq_timeout;
7139 
7140     bfqd->bfq_large_burst_thresh = 8;
7141     bfqd->bfq_burst_interval = msecs_to_jiffies(180);
7142 
7143     bfqd->low_latency = true;
7144 
7145     /*
7146      * Trade-off between responsiveness and fairness.
7147      */
7148     bfqd->bfq_wr_coeff = 30;
7149     bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
7150     bfqd->bfq_wr_max_time = 0;
7151     bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
7152     bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
7153     bfqd->bfq_wr_max_softrt_rate = 7000; /*
7154                           * Approximate rate required
7155                           * to playback or record a
7156                           * high-definition compressed
7157                           * video.
7158                           */
7159     bfqd->wr_busy_queues = 0;
7160 
7161     /*
7162      * Begin by assuming, optimistically, that the device peak
7163      * rate is equal to 2/3 of the highest reference rate.
7164      */
7165     bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
7166         ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
7167     bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
7168 
7169     spin_lock_init(&bfqd->lock);
7170 
7171     /*
7172      * The invocation of the next bfq_create_group_hierarchy
7173      * function is the head of a chain of function calls
7174      * (bfq_create_group_hierarchy->blkcg_activate_policy->
7175      * blk_mq_freeze_queue) that may lead to the invocation of the
7176      * has_work hook function. For this reason,
7177      * bfq_create_group_hierarchy is invoked only after all
7178      * scheduler data has been initialized, apart from the fields
7179      * that can be initialized only after invoking
7180      * bfq_create_group_hierarchy. This, in particular, enables
7181      * has_work to correctly return false. Of course, to avoid
7182      * other inconsistencies, the blk-mq stack must then refrain
7183      * from invoking further scheduler hooks before this init
7184      * function is finished.
7185      */
7186     bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
7187     if (!bfqd->root_group)
7188         goto out_free;
7189     bfq_init_root_group(bfqd->root_group, bfqd);
7190     bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
7191 
7192     /* We dispatch from request queue wide instead of hw queue */
7193     blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
7194 
7195     wbt_disable_default(q);
7196     blk_stat_enable_accounting(q);
7197 
7198     return 0;
7199 
7200 out_free:
7201     kfree(bfqd);
7202     kobject_put(&eq->kobj);
7203     return -ENOMEM;
7204 }
7205 
7206 static void bfq_slab_kill(void)
7207 {
7208     kmem_cache_destroy(bfq_pool);
7209 }
7210 
7211 static int __init bfq_slab_setup(void)
7212 {
7213     bfq_pool = KMEM_CACHE(bfq_queue, 0);
7214     if (!bfq_pool)
7215         return -ENOMEM;
7216     return 0;
7217 }
7218 
7219 static ssize_t bfq_var_show(unsigned int var, char *page)
7220 {
7221     return sprintf(page, "%u\n", var);
7222 }
7223 
7224 static int bfq_var_store(unsigned long *var, const char *page)
7225 {
7226     unsigned long new_val;
7227     int ret = kstrtoul(page, 10, &new_val);
7228 
7229     if (ret)
7230         return ret;
7231     *var = new_val;
7232     return 0;
7233 }
7234 
7235 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                \
7236 static ssize_t __FUNC(struct elevator_queue *e, char *page)     \
7237 {                                   \
7238     struct bfq_data *bfqd = e->elevator_data;           \
7239     u64 __data = __VAR;                     \
7240     if (__CONV == 1)                        \
7241         __data = jiffies_to_msecs(__data);          \
7242     else if (__CONV == 2)                       \
7243         __data = div_u64(__data, NSEC_PER_MSEC);        \
7244     return bfq_var_show(__data, (page));                \
7245 }
7246 SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
7247 SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
7248 SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
7249 SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
7250 SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
7251 SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
7252 SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
7253 SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
7254 SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
7255 #undef SHOW_FUNCTION
7256 
7257 #define USEC_SHOW_FUNCTION(__FUNC, __VAR)               \
7258 static ssize_t __FUNC(struct elevator_queue *e, char *page)     \
7259 {                                   \
7260     struct bfq_data *bfqd = e->elevator_data;           \
7261     u64 __data = __VAR;                     \
7262     __data = div_u64(__data, NSEC_PER_USEC);            \
7263     return bfq_var_show(__data, (page));                \
7264 }
7265 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
7266 #undef USEC_SHOW_FUNCTION
7267 
7268 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)         \
7269 static ssize_t                              \
7270 __FUNC(struct elevator_queue *e, const char *page, size_t count)    \
7271 {                                   \
7272     struct bfq_data *bfqd = e->elevator_data;           \
7273     unsigned long __data, __min = (MIN), __max = (MAX);     \
7274     int ret;                            \
7275                                     \
7276     ret = bfq_var_store(&__data, (page));               \
7277     if (ret)                            \
7278         return ret;                     \
7279     if (__data < __min)                     \
7280         __data = __min;                     \
7281     else if (__data > __max)                    \
7282         __data = __max;                     \
7283     if (__CONV == 1)                        \
7284         *(__PTR) = msecs_to_jiffies(__data);            \
7285     else if (__CONV == 2)                       \
7286         *(__PTR) = (u64)__data * NSEC_PER_MSEC;         \
7287     else                                \
7288         *(__PTR) = __data;                  \
7289     return count;                           \
7290 }
7291 STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
7292         INT_MAX, 2);
7293 STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
7294         INT_MAX, 2);
7295 STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
7296 STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
7297         INT_MAX, 0);
7298 STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
7299 #undef STORE_FUNCTION
7300 
7301 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)            \
7302 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
7303 {                                   \
7304     struct bfq_data *bfqd = e->elevator_data;           \
7305     unsigned long __data, __min = (MIN), __max = (MAX);     \
7306     int ret;                            \
7307                                     \
7308     ret = bfq_var_store(&__data, (page));               \
7309     if (ret)                            \
7310         return ret;                     \
7311     if (__data < __min)                     \
7312         __data = __min;                     \
7313     else if (__data > __max)                    \
7314         __data = __max;                     \
7315     *(__PTR) = (u64)__data * NSEC_PER_USEC;             \
7316     return count;                           \
7317 }
7318 USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
7319             UINT_MAX);
7320 #undef USEC_STORE_FUNCTION
7321 
7322 static ssize_t bfq_max_budget_store(struct elevator_queue *e,
7323                     const char *page, size_t count)
7324 {
7325     struct bfq_data *bfqd = e->elevator_data;
7326     unsigned long __data;
7327     int ret;
7328 
7329     ret = bfq_var_store(&__data, (page));
7330     if (ret)
7331         return ret;
7332 
7333     if (__data == 0)
7334         bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7335     else {
7336         if (__data > INT_MAX)
7337             __data = INT_MAX;
7338         bfqd->bfq_max_budget = __data;
7339     }
7340 
7341     bfqd->bfq_user_max_budget = __data;
7342 
7343     return count;
7344 }
7345 
7346 /*
7347  * Leaving this name to preserve name compatibility with cfq
7348  * parameters, but this timeout is used for both sync and async.
7349  */
7350 static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
7351                       const char *page, size_t count)
7352 {
7353     struct bfq_data *bfqd = e->elevator_data;
7354     unsigned long __data;
7355     int ret;
7356 
7357     ret = bfq_var_store(&__data, (page));
7358     if (ret)
7359         return ret;
7360 
7361     if (__data < 1)
7362         __data = 1;
7363     else if (__data > INT_MAX)
7364         __data = INT_MAX;
7365 
7366     bfqd->bfq_timeout = msecs_to_jiffies(__data);
7367     if (bfqd->bfq_user_max_budget == 0)
7368         bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7369 
7370     return count;
7371 }
7372 
7373 static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
7374                      const char *page, size_t count)
7375 {
7376     struct bfq_data *bfqd = e->elevator_data;
7377     unsigned long __data;
7378     int ret;
7379 
7380     ret = bfq_var_store(&__data, (page));
7381     if (ret)
7382         return ret;
7383 
7384     if (__data > 1)
7385         __data = 1;
7386     if (!bfqd->strict_guarantees && __data == 1
7387         && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
7388         bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
7389 
7390     bfqd->strict_guarantees = __data;
7391 
7392     return count;
7393 }
7394 
7395 static ssize_t bfq_low_latency_store(struct elevator_queue *e,
7396                      const char *page, size_t count)
7397 {
7398     struct bfq_data *bfqd = e->elevator_data;
7399     unsigned long __data;
7400     int ret;
7401 
7402     ret = bfq_var_store(&__data, (page));
7403     if (ret)
7404         return ret;
7405 
7406     if (__data > 1)
7407         __data = 1;
7408     if (__data == 0 && bfqd->low_latency != 0)
7409         bfq_end_wr(bfqd);
7410     bfqd->low_latency = __data;
7411 
7412     return count;
7413 }
7414 
7415 #define BFQ_ATTR(name) \
7416     __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
7417 
7418 static struct elv_fs_entry bfq_attrs[] = {
7419     BFQ_ATTR(fifo_expire_sync),
7420     BFQ_ATTR(fifo_expire_async),
7421     BFQ_ATTR(back_seek_max),
7422     BFQ_ATTR(back_seek_penalty),
7423     BFQ_ATTR(slice_idle),
7424     BFQ_ATTR(slice_idle_us),
7425     BFQ_ATTR(max_budget),
7426     BFQ_ATTR(timeout_sync),
7427     BFQ_ATTR(strict_guarantees),
7428     BFQ_ATTR(low_latency),
7429     __ATTR_NULL
7430 };
7431 
7432 static struct elevator_type iosched_bfq_mq = {
7433     .ops = {
7434         .limit_depth        = bfq_limit_depth,
7435         .prepare_request    = bfq_prepare_request,
7436         .requeue_request        = bfq_finish_requeue_request,
7437         .finish_request     = bfq_finish_request,
7438         .exit_icq       = bfq_exit_icq,
7439         .insert_requests    = bfq_insert_requests,
7440         .dispatch_request   = bfq_dispatch_request,
7441         .next_request       = elv_rb_latter_request,
7442         .former_request     = elv_rb_former_request,
7443         .allow_merge        = bfq_allow_bio_merge,
7444         .bio_merge      = bfq_bio_merge,
7445         .request_merge      = bfq_request_merge,
7446         .requests_merged    = bfq_requests_merged,
7447         .request_merged     = bfq_request_merged,
7448         .has_work       = bfq_has_work,
7449         .depth_updated      = bfq_depth_updated,
7450         .init_hctx      = bfq_init_hctx,
7451         .init_sched     = bfq_init_queue,
7452         .exit_sched     = bfq_exit_queue,
7453     },
7454 
7455     .icq_size =     sizeof(struct bfq_io_cq),
7456     .icq_align =        __alignof__(struct bfq_io_cq),
7457     .elevator_attrs =   bfq_attrs,
7458     .elevator_name =    "bfq",
7459     .elevator_owner =   THIS_MODULE,
7460 };
7461 MODULE_ALIAS("bfq-iosched");
7462 
7463 static int __init bfq_init(void)
7464 {
7465     int ret;
7466 
7467 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7468     ret = blkcg_policy_register(&blkcg_policy_bfq);
7469     if (ret)
7470         return ret;
7471 #endif
7472 
7473     ret = -ENOMEM;
7474     if (bfq_slab_setup())
7475         goto err_pol_unreg;
7476 
7477     /*
7478      * Times to load large popular applications for the typical
7479      * systems installed on the reference devices (see the
7480      * comments before the definition of the next
7481      * array). Actually, we use slightly lower values, as the
7482      * estimated peak rate tends to be smaller than the actual
7483      * peak rate.  The reason for this last fact is that estimates
7484      * are computed over much shorter time intervals than the long
7485      * intervals typically used for benchmarking. Why? First, to
7486      * adapt more quickly to variations. Second, because an I/O
7487      * scheduler cannot rely on a peak-rate-evaluation workload to
7488      * be run for a long time.
7489      */
7490     ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
7491     ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
7492 
7493     ret = elv_register(&iosched_bfq_mq);
7494     if (ret)
7495         goto slab_kill;
7496 
7497     return 0;
7498 
7499 slab_kill:
7500     bfq_slab_kill();
7501 err_pol_unreg:
7502 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7503     blkcg_policy_unregister(&blkcg_policy_bfq);
7504 #endif
7505     return ret;
7506 }
7507 
7508 static void __exit bfq_exit(void)
7509 {
7510     elv_unregister(&iosched_bfq_mq);
7511 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7512     blkcg_policy_unregister(&blkcg_policy_bfq);
7513 #endif
7514     bfq_slab_kill();
7515 }
7516 
7517 module_init(bfq_init);
7518 module_exit(bfq_exit);
7519 
7520 MODULE_AUTHOR("Paolo Valente");
7521 MODULE_LICENSE("GPL");
7522 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");