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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Interface for controlling IO bandwidth on a request queue
  *
  * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
  */
 
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/bio.h>
 #include <linux/blktrace_api.h>
 #include "blk.h"
 #include "blk-cgroup-rwstat.h"
 #include "blk-stat.h"
 #include "blk-throttle.h"
 
 /* Max dispatch from a group in 1 round */
 #define THROTL_GRP_QUANTUM 8
 
 /* Total max dispatch from all groups in one round */
 #define THROTL_QUANTUM 32
 
 /* Throttling is performed over a slice and after that slice is renewed */
 #define DFL_THROTL_SLICE_HD (HZ / 10)
 #define DFL_THROTL_SLICE_SSD (HZ / 50)
 #define MAX_THROTL_SLICE (HZ)
 #define MAX_IDLE_TIME (5L * 1000 * 1000) /* 5 s */
 #define MIN_THROTL_BPS (320 * 1024)
 #define MIN_THROTL_IOPS (10)
 #define DFL_LATENCY_TARGET (-1L)
 #define DFL_IDLE_THRESHOLD (0)
 #define DFL_HD_BASELINE_LATENCY (4000L) /* 4ms */
 #define LATENCY_FILTERED_SSD (0)
 /*
  * For HD, very small latency comes from sequential IO. Such IO is helpless to
  * help determine if its IO is impacted by others, hence we ignore the IO
  */
 #define LATENCY_FILTERED_HD (1000L) /* 1ms */
 
 /* A workqueue to queue throttle related work */
 static struct workqueue_struct *kthrotld_workqueue;
 
 #define rb_entry_tg(node)   rb_entry((node), struct throtl_grp, rb_node)
 
 /* We measure latency for request size from <= 4k to >= 1M */
 #define LATENCY_BUCKET_SIZE 9
 
 struct latency_bucket {
     unsigned long total_latency; /* ns / 1024 */
     int samples;
 };
 
 struct avg_latency_bucket {
     unsigned long latency; /* ns / 1024 */
     bool valid;
 };
 
 struct throtl_data
 {
     /* service tree for active throtl groups */
     struct throtl_service_queue service_queue;
 
     struct request_queue *queue;
 
     /* Total Number of queued bios on READ and WRITE lists */
     unsigned int nr_queued[2];
 
     unsigned int throtl_slice;
 
     /* Work for dispatching throttled bios */
     struct work_struct dispatch_work;
     unsigned int limit_index;
     bool limit_valid[LIMIT_CNT];
 
     unsigned long low_upgrade_time;
     unsigned long low_downgrade_time;
 
     unsigned int scale;
 
     struct latency_bucket tmp_buckets[2][LATENCY_BUCKET_SIZE];
     struct avg_latency_bucket avg_buckets[2][LATENCY_BUCKET_SIZE];
     struct latency_bucket __percpu *latency_buckets[2];
     unsigned long last_calculate_time;
     unsigned long filtered_latency;
 
     bool track_bio_latency;
 };
 
 static void throtl_pending_timer_fn(struct timer_list *t);
 
 static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
 {
     return pd_to_blkg(&tg->pd);
 }
 
 /**
  * sq_to_tg - return the throl_grp the specified service queue belongs to
  * @sq: the throtl_service_queue of interest
  *
  * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
  * embedded in throtl_data, %NULL is returned.
  */
 static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
 {
     if (sq && sq->parent_sq)
         return container_of(sq, struct throtl_grp, service_queue);
     else
         return NULL;
 }
 
 /**
  * sq_to_td - return throtl_data the specified service queue belongs to
  * @sq: the throtl_service_queue of interest
  *
  * A service_queue can be embedded in either a throtl_grp or throtl_data.
  * Determine the associated throtl_data accordingly and return it.
  */
 static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
 {
     struct throtl_grp *tg = sq_to_tg(sq);
 
     if (tg)
         return tg->td;
     else
         return container_of(sq, struct throtl_data, service_queue);
 }
 
 /*
  * cgroup's limit in LIMIT_MAX is scaled if low limit is set. This scale is to
  * make the IO dispatch more smooth.
  * Scale up: linearly scale up according to lapsed time since upgrade. For
  *           every throtl_slice, the limit scales up 1/2 .low limit till the
  *           limit hits .max limit
  * Scale down: exponentially scale down if a cgroup doesn't hit its .low limit
  */
 static uint64_t throtl_adjusted_limit(uint64_t low, struct throtl_data *td)
 {
     /* arbitrary value to avoid too big scale */
     if (td->scale < 4096 && time_after_eq(jiffies,
         td->low_upgrade_time + td->scale * td->throtl_slice))
         td->scale = (jiffies - td->low_upgrade_time) / td->throtl_slice;
 
     return low + (low >> 1) * td->scale;
 }
 
 static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
 {
     struct blkcg_gq *blkg = tg_to_blkg(tg);
     struct throtl_data *td;
     uint64_t ret;
 
     if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
         return U64_MAX;
 
     td = tg->td;
     ret = tg->bps[rw][td->limit_index];
     if (ret == 0 && td->limit_index == LIMIT_LOW) {
         /* intermediate node or iops isn't 0 */
         if (!list_empty(&blkg->blkcg->css.children) ||
             tg->iops[rw][td->limit_index])
             return U64_MAX;
         else
             return MIN_THROTL_BPS;
     }
 
     if (td->limit_index == LIMIT_MAX && tg->bps[rw][LIMIT_LOW] &&
         tg->bps[rw][LIMIT_LOW] != tg->bps[rw][LIMIT_MAX]) {
         uint64_t adjusted;
 
         adjusted = throtl_adjusted_limit(tg->bps[rw][LIMIT_LOW], td);
         ret = min(tg->bps[rw][LIMIT_MAX], adjusted);
     }
     return ret;
 }
 
 static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
 {
     struct blkcg_gq *blkg = tg_to_blkg(tg);
     struct throtl_data *td;
     unsigned int ret;
 
     if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
         return UINT_MAX;
 
     td = tg->td;
     ret = tg->iops[rw][td->limit_index];
     if (ret == 0 && tg->td->limit_index == LIMIT_LOW) {
         /* intermediate node or bps isn't 0 */
         if (!list_empty(&blkg->blkcg->css.children) ||
             tg->bps[rw][td->limit_index])
             return UINT_MAX;
         else
             return MIN_THROTL_IOPS;
     }
 
     if (td->limit_index == LIMIT_MAX && tg->iops[rw][LIMIT_LOW] &&
         tg->iops[rw][LIMIT_LOW] != tg->iops[rw][LIMIT_MAX]) {
         uint64_t adjusted;
 
         adjusted = throtl_adjusted_limit(tg->iops[rw][LIMIT_LOW], td);
         if (adjusted > UINT_MAX)
             adjusted = UINT_MAX;
         ret = min_t(unsigned int, tg->iops[rw][LIMIT_MAX], adjusted);
     }
     return ret;
 }
 
 #define request_bucket_index(sectors) \
     clamp_t(int, order_base_2(sectors) - 3, 0, LATENCY_BUCKET_SIZE - 1)
 
 /**
  * throtl_log - log debug message via blktrace
  * @sq: the service_queue being reported
  * @fmt: printf format string
  * @args: printf args
  *
  * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
  * throtl_grp; otherwise, just "throtl".
  */
 #define throtl_log(sq, fmt, args...)    do {                \
     struct throtl_grp *__tg = sq_to_tg((sq));           \
     struct throtl_data *__td = sq_to_td((sq));          \
                                     \
     (void)__td;                         \
     if (likely(!blk_trace_note_message_enabled(__td->queue)))   \
         break;                          \
     if ((__tg)) {                           \
         blk_add_cgroup_trace_msg(__td->queue,           \
             &tg_to_blkg(__tg)->blkcg->css, "throtl " fmt, ##args);\
     } else {                            \
         blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);  \
     }                               \
 } while (0)
 
 static inline unsigned int throtl_bio_data_size(struct bio *bio)
 {
     /* assume it's one sector */
     if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
         return 512;
     return bio->bi_iter.bi_size;
 }
 
 static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
 {
     INIT_LIST_HEAD(&qn->node);
     bio_list_init(&qn->bios);
     qn->tg = tg;
 }
 
 /**
  * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
  * @bio: bio being added
  * @qn: qnode to add bio to
  * @queued: the service_queue->queued[] list @qn belongs to
  *
  * Add @bio to @qn and put @qn on @queued if it's not already on.
  * @qn->tg's reference count is bumped when @qn is activated.  See the
  * comment on top of throtl_qnode definition for details.
  */
 static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
                  struct list_head *queued)
 {
     bio_list_add(&qn->bios, bio);
     if (list_empty(&qn->node)) {
         list_add_tail(&qn->node, queued);
         blkg_get(tg_to_blkg(qn->tg));
     }
 }
 
 /**
  * throtl_peek_queued - peek the first bio on a qnode list
  * @queued: the qnode list to peek
  */
 static struct bio *throtl_peek_queued(struct list_head *queued)
 {
     struct throtl_qnode *qn;
     struct bio *bio;
 
     if (list_empty(queued))
         return NULL;
 
     qn = list_first_entry(queued, struct throtl_qnode, node);
     bio = bio_list_peek(&qn->bios);
     WARN_ON_ONCE(!bio);
     return bio;
 }
 
 /**
  * throtl_pop_queued - pop the first bio form a qnode list
  * @queued: the qnode list to pop a bio from
  * @tg_to_put: optional out argument for throtl_grp to put
  *
  * Pop the first bio from the qnode list @queued.  After popping, the first
  * qnode is removed from @queued if empty or moved to the end of @queued so
  * that the popping order is round-robin.
  *
  * When the first qnode is removed, its associated throtl_grp should be put
  * too.  If @tg_to_put is NULL, this function automatically puts it;
  * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
  * responsible for putting it.
  */
 static struct bio *throtl_pop_queued(struct list_head *queued,
                      struct throtl_grp **tg_to_put)
 {
     struct throtl_qnode *qn;
     struct bio *bio;
 
     if (list_empty(queued))
         return NULL;
 
     qn = list_first_entry(queued, struct throtl_qnode, node);
     bio = bio_list_pop(&qn->bios);
     WARN_ON_ONCE(!bio);
 
     if (bio_list_empty(&qn->bios)) {
         list_del_init(&qn->node);
         if (tg_to_put)
             *tg_to_put = qn->tg;
         else
             blkg_put(tg_to_blkg(qn->tg));
     } else {
         list_move_tail(&qn->node, queued);
     }
 
     return bio;
 }
 
 /* init a service_queue, assumes the caller zeroed it */
 static void throtl_service_queue_init(struct throtl_service_queue *sq)
 {
     INIT_LIST_HEAD(&sq->queued[0]);
     INIT_LIST_HEAD(&sq->queued[1]);
     sq->pending_tree = RB_ROOT_CACHED;
     timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
 }
 
 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp,
                         struct request_queue *q,
                         struct blkcg *blkcg)
 {
     struct throtl_grp *tg;
     int rw;
 
     tg = kzalloc_node(sizeof(*tg), gfp, q->node);
     if (!tg)
         return NULL;
 
     if (blkg_rwstat_init(&tg->stat_bytes, gfp))
         goto err_free_tg;
 
     if (blkg_rwstat_init(&tg->stat_ios, gfp))
         goto err_exit_stat_bytes;
 
     throtl_service_queue_init(&tg->service_queue);
 
     for (rw = READ; rw <= WRITE; rw++) {
         throtl_qnode_init(&tg->qnode_on_self[rw], tg);
         throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
     }
 
     RB_CLEAR_NODE(&tg->rb_node);
     tg->bps[READ][LIMIT_MAX] = U64_MAX;
     tg->bps[WRITE][LIMIT_MAX] = U64_MAX;
     tg->iops[READ][LIMIT_MAX] = UINT_MAX;
     tg->iops[WRITE][LIMIT_MAX] = UINT_MAX;
     tg->bps_conf[READ][LIMIT_MAX] = U64_MAX;
     tg->bps_conf[WRITE][LIMIT_MAX] = U64_MAX;
     tg->iops_conf[READ][LIMIT_MAX] = UINT_MAX;
     tg->iops_conf[WRITE][LIMIT_MAX] = UINT_MAX;
     /* LIMIT_LOW will have default value 0 */
 
     tg->latency_target = DFL_LATENCY_TARGET;
     tg->latency_target_conf = DFL_LATENCY_TARGET;
     tg->idletime_threshold = DFL_IDLE_THRESHOLD;
     tg->idletime_threshold_conf = DFL_IDLE_THRESHOLD;
 
     return &tg->pd;
 
 err_exit_stat_bytes:
     blkg_rwstat_exit(&tg->stat_bytes);
 err_free_tg:
     kfree(tg);
     return NULL;
 }
 
 static void throtl_pd_init(struct blkg_policy_data *pd)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
     struct blkcg_gq *blkg = tg_to_blkg(tg);
     struct throtl_data *td = blkg->q->td;
     struct throtl_service_queue *sq = &tg->service_queue;
 
     /*
      * If on the default hierarchy, we switch to properly hierarchical
      * behavior where limits on a given throtl_grp are applied to the
      * whole subtree rather than just the group itself.  e.g. If 16M
      * read_bps limit is set on the root group, the whole system can't
      * exceed 16M for the device.
      *
      * If not on the default hierarchy, the broken flat hierarchy
      * behavior is retained where all throtl_grps are treated as if
      * they're all separate root groups right below throtl_data.
      * Limits of a group don't interact with limits of other groups
      * regardless of the position of the group in the hierarchy.
      */
     sq->parent_sq = &td->service_queue;
     if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
         sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
     tg->td = td;
 }
 
 /*
  * Set has_rules[] if @tg or any of its parents have limits configured.
  * This doesn't require walking up to the top of the hierarchy as the
  * parent's has_rules[] is guaranteed to be correct.
  */
 static void tg_update_has_rules(struct throtl_grp *tg)
 {
     struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
     struct throtl_data *td = tg->td;
     int rw;
     int has_iops_limit = 0;
 
     for (rw = READ; rw <= WRITE; rw++) {
         unsigned int iops_limit = tg_iops_limit(tg, rw);
 
         tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
             (td->limit_valid[td->limit_index] &&
              (tg_bps_limit(tg, rw) != U64_MAX ||
               iops_limit != UINT_MAX));
 
         if (iops_limit != UINT_MAX)
             has_iops_limit = 1;
     }
 
     if (has_iops_limit)
         tg->flags |= THROTL_TG_HAS_IOPS_LIMIT;
     else
         tg->flags &= ~THROTL_TG_HAS_IOPS_LIMIT;
 }
 
 static void throtl_pd_online(struct blkg_policy_data *pd)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
     /*
      * We don't want new groups to escape the limits of its ancestors.
      * Update has_rules[] after a new group is brought online.
      */
     tg_update_has_rules(tg);
 }
 
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 static void blk_throtl_update_limit_valid(struct throtl_data *td)
 {
     struct cgroup_subsys_state *pos_css;
     struct blkcg_gq *blkg;
     bool low_valid = false;
 
     rcu_read_lock();
     blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
         struct throtl_grp *tg = blkg_to_tg(blkg);
 
         if (tg->bps[READ][LIMIT_LOW] || tg->bps[WRITE][LIMIT_LOW] ||
             tg->iops[READ][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) {
             low_valid = true;
             break;
         }
     }
     rcu_read_unlock();
 
     td->limit_valid[LIMIT_LOW] = low_valid;
 }
 #else
 static inline void blk_throtl_update_limit_valid(struct throtl_data *td)
 {
 }
 #endif
 
 static void throtl_upgrade_state(struct throtl_data *td);
 static void throtl_pd_offline(struct blkg_policy_data *pd)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
 
     tg->bps[READ][LIMIT_LOW] = 0;
     tg->bps[WRITE][LIMIT_LOW] = 0;
     tg->iops[READ][LIMIT_LOW] = 0;
     tg->iops[WRITE][LIMIT_LOW] = 0;
 
     blk_throtl_update_limit_valid(tg->td);
 
     if (!tg->td->limit_valid[tg->td->limit_index])
         throtl_upgrade_state(tg->td);
 }
 
 static void throtl_pd_free(struct blkg_policy_data *pd)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
 
     del_timer_sync(&tg->service_queue.pending_timer);
     blkg_rwstat_exit(&tg->stat_bytes);
     blkg_rwstat_exit(&tg->stat_ios);
     kfree(tg);
 }
 
 static struct throtl_grp *
 throtl_rb_first(struct throtl_service_queue *parent_sq)
 {
     struct rb_node *n;
 
     n = rb_first_cached(&parent_sq->pending_tree);
     WARN_ON_ONCE(!n);
     if (!n)
         return NULL;
     return rb_entry_tg(n);
 }
 
 static void throtl_rb_erase(struct rb_node *n,
                 struct throtl_service_queue *parent_sq)
 {
     rb_erase_cached(n, &parent_sq->pending_tree);
     RB_CLEAR_NODE(n);
     --parent_sq->nr_pending;
 }
 
 static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
 {
     struct throtl_grp *tg;
 
     tg = throtl_rb_first(parent_sq);
     if (!tg)
         return;
 
     parent_sq->first_pending_disptime = tg->disptime;
 }
 
 static void tg_service_queue_add(struct throtl_grp *tg)
 {
     struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
     struct rb_node **node = &parent_sq->pending_tree.rb_root.rb_node;
     struct rb_node *parent = NULL;
     struct throtl_grp *__tg;
     unsigned long key = tg->disptime;
     bool leftmost = true;
 
     while (*node != NULL) {
         parent = *node;
         __tg = rb_entry_tg(parent);
 
         if (time_before(key, __tg->disptime))
             node = &parent->rb_left;
         else {
             node = &parent->rb_right;
             leftmost = false;
         }
     }
 
     rb_link_node(&tg->rb_node, parent, node);
     rb_insert_color_cached(&tg->rb_node, &parent_sq->pending_tree,
                    leftmost);
 }
 
 static void throtl_enqueue_tg(struct throtl_grp *tg)
 {
     if (!(tg->flags & THROTL_TG_PENDING)) {
         tg_service_queue_add(tg);
         tg->flags |= THROTL_TG_PENDING;
         tg->service_queue.parent_sq->nr_pending++;
     }
 }
 
 static void throtl_dequeue_tg(struct throtl_grp *tg)
 {
     if (tg->flags & THROTL_TG_PENDING) {
         throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
         tg->flags &= ~THROTL_TG_PENDING;
     }
 }
 
 /* Call with queue lock held */
 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
                       unsigned long expires)
 {
     unsigned long max_expire = jiffies + 8 * sq_to_td(sq)->throtl_slice;
 
     /*
      * Since we are adjusting the throttle limit dynamically, the sleep
      * time calculated according to previous limit might be invalid. It's
      * possible the cgroup sleep time is very long and no other cgroups
      * have IO running so notify the limit changes. Make sure the cgroup
      * doesn't sleep too long to avoid the missed notification.
      */
     if (time_after(expires, max_expire))
         expires = max_expire;
     mod_timer(&sq->pending_timer, expires);
     throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
            expires - jiffies, jiffies);
 }
 
 /**
  * throtl_schedule_next_dispatch - schedule the next dispatch cycle
  * @sq: the service_queue to schedule dispatch for
  * @force: force scheduling
  *
  * Arm @sq->pending_timer so that the next dispatch cycle starts on the
  * dispatch time of the first pending child.  Returns %true if either timer
  * is armed or there's no pending child left.  %false if the current
  * dispatch window is still open and the caller should continue
  * dispatching.
  *
  * If @force is %true, the dispatch timer is always scheduled and this
  * function is guaranteed to return %true.  This is to be used when the
  * caller can't dispatch itself and needs to invoke pending_timer
  * unconditionally.  Note that forced scheduling is likely to induce short
  * delay before dispatch starts even if @sq->first_pending_disptime is not
  * in the future and thus shouldn't be used in hot paths.
  */
 static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
                       bool force)
 {
     /* any pending children left? */
     if (!sq->nr_pending)
         return true;
 
     update_min_dispatch_time(sq);
 
     /* is the next dispatch time in the future? */
     if (force || time_after(sq->first_pending_disptime, jiffies)) {
         throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
         return true;
     }
 
     /* tell the caller to continue dispatching */
     return false;
 }
 
 static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
         bool rw, unsigned long start)
 {
     tg->bytes_disp[rw] = 0;
     tg->io_disp[rw] = 0;
 
     /*
      * Previous slice has expired. We must have trimmed it after last
      * bio dispatch. That means since start of last slice, we never used
      * that bandwidth. Do try to make use of that bandwidth while giving
      * credit.
      */
     if (time_after_eq(start, tg->slice_start[rw]))
         tg->slice_start[rw] = start;
 
     tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
     throtl_log(&tg->service_queue,
            "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
            rw == READ ? 'R' : 'W', tg->slice_start[rw],
            tg->slice_end[rw], jiffies);
 }
 
 static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
 {
     tg->bytes_disp[rw] = 0;
     tg->io_disp[rw] = 0;
     tg->slice_start[rw] = jiffies;
     tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
 
     throtl_log(&tg->service_queue,
            "[%c] new slice start=%lu end=%lu jiffies=%lu",
            rw == READ ? 'R' : 'W', tg->slice_start[rw],
            tg->slice_end[rw], jiffies);
 }
 
 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
                     unsigned long jiffy_end)
 {
     tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
 }
 
 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
                        unsigned long jiffy_end)
 {
     throtl_set_slice_end(tg, rw, jiffy_end);
     throtl_log(&tg->service_queue,
            "[%c] extend slice start=%lu end=%lu jiffies=%lu",
            rw == READ ? 'R' : 'W', tg->slice_start[rw],
            tg->slice_end[rw], jiffies);
 }
 
 /* Determine if previously allocated or extended slice is complete or not */
 static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
 {
     if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
         return false;
 
     return true;
 }
 
 /* Trim the used slices and adjust slice start accordingly */
 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 {
     unsigned long nr_slices, time_elapsed, io_trim;
     u64 bytes_trim, tmp;
 
     BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
 
     /*
      * If bps are unlimited (-1), then time slice don't get
      * renewed. Don't try to trim the slice if slice is used. A new
      * slice will start when appropriate.
      */
     if (throtl_slice_used(tg, rw))
         return;
 
     /*
      * A bio has been dispatched. Also adjust slice_end. It might happen
      * that initially cgroup limit was very low resulting in high
      * slice_end, but later limit was bumped up and bio was dispatched
      * sooner, then we need to reduce slice_end. A high bogus slice_end
      * is bad because it does not allow new slice to start.
      */
 
     throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);
 
     time_elapsed = jiffies - tg->slice_start[rw];
 
     nr_slices = time_elapsed / tg->td->throtl_slice;
 
     if (!nr_slices)
         return;
     tmp = tg_bps_limit(tg, rw) * tg->td->throtl_slice * nr_slices;
     do_div(tmp, HZ);
     bytes_trim = tmp;
 
     io_trim = (tg_iops_limit(tg, rw) * tg->td->throtl_slice * nr_slices) /
         HZ;
 
     if (!bytes_trim && !io_trim)
         return;
 
     if (tg->bytes_disp[rw] >= bytes_trim)
         tg->bytes_disp[rw] -= bytes_trim;
     else
         tg->bytes_disp[rw] = 0;
 
     if (tg->io_disp[rw] >= io_trim)
         tg->io_disp[rw] -= io_trim;
     else
         tg->io_disp[rw] = 0;
 
     tg->slice_start[rw] += nr_slices * tg->td->throtl_slice;
 
     throtl_log(&tg->service_queue,
            "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
            rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
            tg->slice_start[rw], tg->slice_end[rw], jiffies);
 }
 
 static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
                   u32 iops_limit, unsigned long *wait)
 {
     bool rw = bio_data_dir(bio);
     unsigned int io_allowed;
     unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
     u64 tmp;
 
     if (iops_limit == UINT_MAX) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     jiffy_elapsed = jiffies - tg->slice_start[rw];
 
     /* Round up to the next throttle slice, wait time must be nonzero */
     jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);
 
     /*
      * jiffy_elapsed_rnd should not be a big value as minimum iops can be
      * 1 then at max jiffy elapsed should be equivalent of 1 second as we
      * will allow dispatch after 1 second and after that slice should
      * have been trimmed.
      */
 
     tmp = (u64)iops_limit * jiffy_elapsed_rnd;
     do_div(tmp, HZ);
 
     if (tmp > UINT_MAX)
         io_allowed = UINT_MAX;
     else
         io_allowed = tmp;
 
     if (tg->io_disp[rw] + 1 <= io_allowed) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     /* Calc approx time to dispatch */
     jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed;
 
     if (wait)
         *wait = jiffy_wait;
     return false;
 }
 
 static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
                  u64 bps_limit, unsigned long *wait)
 {
     bool rw = bio_data_dir(bio);
     u64 bytes_allowed, extra_bytes, tmp;
     unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
     unsigned int bio_size = throtl_bio_data_size(bio);
 
     /* no need to throttle if this bio's bytes have been accounted */
     if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
 
     /* Slice has just started. Consider one slice interval */
     if (!jiffy_elapsed)
         jiffy_elapsed_rnd = tg->td->throtl_slice;
 
     jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
 
     tmp = bps_limit * jiffy_elapsed_rnd;
     do_div(tmp, HZ);
     bytes_allowed = tmp;
 
     if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     /* Calc approx time to dispatch */
     extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
     jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit);
 
     if (!jiffy_wait)
         jiffy_wait = 1;
 
     /*
      * This wait time is without taking into consideration the rounding
      * up we did. Add that time also.
      */
     jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
     if (wait)
         *wait = jiffy_wait;
     return false;
 }
 
 /*
  * Returns whether one can dispatch a bio or not. Also returns approx number
  * of jiffies to wait before this bio is with-in IO rate and can be dispatched
  */
 static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
                 unsigned long *wait)
 {
     bool rw = bio_data_dir(bio);
     unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
     u64 bps_limit = tg_bps_limit(tg, rw);
     u32 iops_limit = tg_iops_limit(tg, rw);
 
     /*
      * Currently whole state machine of group depends on first bio
      * queued in the group bio list. So one should not be calling
      * this function with a different bio if there are other bios
      * queued.
      */
     BUG_ON(tg->service_queue.nr_queued[rw] &&
            bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
 
     /* If tg->bps = -1, then BW is unlimited */
     if ((bps_limit == U64_MAX && iops_limit == UINT_MAX) ||
         tg->flags & THROTL_TG_CANCELING) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     /*
      * If previous slice expired, start a new one otherwise renew/extend
      * existing slice to make sure it is at least throtl_slice interval
      * long since now. New slice is started only for empty throttle group.
      * If there is queued bio, that means there should be an active
      * slice and it should be extended instead.
      */
     if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
         throtl_start_new_slice(tg, rw);
     else {
         if (time_before(tg->slice_end[rw],
             jiffies + tg->td->throtl_slice))
             throtl_extend_slice(tg, rw,
                 jiffies + tg->td->throtl_slice);
     }
 
     if (tg_with_in_bps_limit(tg, bio, bps_limit, &bps_wait) &&
         tg_with_in_iops_limit(tg, bio, iops_limit, &iops_wait)) {
         if (wait)
             *wait = 0;
         return true;
     }
 
     max_wait = max(bps_wait, iops_wait);
 
     if (wait)
         *wait = max_wait;
 
     if (time_before(tg->slice_end[rw], jiffies + max_wait))
         throtl_extend_slice(tg, rw, jiffies + max_wait);
 
     return false;
 }
 
 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
 {
     bool rw = bio_data_dir(bio);
     unsigned int bio_size = throtl_bio_data_size(bio);
 
     /* Charge the bio to the group */
     if (!bio_flagged(bio, BIO_THROTTLED)) {
         tg->bytes_disp[rw] += bio_size;
         tg->last_bytes_disp[rw] += bio_size;
     }
 
     tg->io_disp[rw]++;
     tg->last_io_disp[rw]++;
 
     /*
      * BIO_THROTTLED is used to prevent the same bio to be throttled
      * more than once as a throttled bio will go through blk-throtl the
      * second time when it eventually gets issued.  Set it when a bio
      * is being charged to a tg.
      */
     if (!bio_flagged(bio, BIO_THROTTLED))
         bio_set_flag(bio, BIO_THROTTLED);
 }
 
 /**
  * throtl_add_bio_tg - add a bio to the specified throtl_grp
  * @bio: bio to add
  * @qn: qnode to use
  * @tg: the target throtl_grp
  *
  * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
  * tg->qnode_on_self[] is used.
  */
 static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
                   struct throtl_grp *tg)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     bool rw = bio_data_dir(bio);
 
     if (!qn)
         qn = &tg->qnode_on_self[rw];
 
     /*
      * If @tg doesn't currently have any bios queued in the same
      * direction, queueing @bio can change when @tg should be
      * dispatched.  Mark that @tg was empty.  This is automatically
      * cleared on the next tg_update_disptime().
      */
     if (!sq->nr_queued[rw])
         tg->flags |= THROTL_TG_WAS_EMPTY;
 
     throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
 
     sq->nr_queued[rw]++;
     throtl_enqueue_tg(tg);
 }
 
 static void tg_update_disptime(struct throtl_grp *tg)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
     struct bio *bio;
 
     bio = throtl_peek_queued(&sq->queued[READ]);
     if (bio)
         tg_may_dispatch(tg, bio, &read_wait);
 
     bio = throtl_peek_queued(&sq->queued[WRITE]);
     if (bio)
         tg_may_dispatch(tg, bio, &write_wait);
 
     min_wait = min(read_wait, write_wait);
     disptime = jiffies + min_wait;
 
     /* Update dispatch time */
     throtl_dequeue_tg(tg);
     tg->disptime = disptime;
     throtl_enqueue_tg(tg);
 
     /* see throtl_add_bio_tg() */
     tg->flags &= ~THROTL_TG_WAS_EMPTY;
 }
 
 static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
                     struct throtl_grp *parent_tg, bool rw)
 {
     if (throtl_slice_used(parent_tg, rw)) {
         throtl_start_new_slice_with_credit(parent_tg, rw,
                 child_tg->slice_start[rw]);
     }
 
 }
 
 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     struct throtl_service_queue *parent_sq = sq->parent_sq;
     struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
     struct throtl_grp *tg_to_put = NULL;
     struct bio *bio;
 
     /*
      * @bio is being transferred from @tg to @parent_sq.  Popping a bio
      * from @tg may put its reference and @parent_sq might end up
      * getting released prematurely.  Remember the tg to put and put it
      * after @bio is transferred to @parent_sq.
      */
     bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
     sq->nr_queued[rw]--;
 
     throtl_charge_bio(tg, bio);
 
     /*
      * If our parent is another tg, we just need to transfer @bio to
      * the parent using throtl_add_bio_tg().  If our parent is
      * @td->service_queue, @bio is ready to be issued.  Put it on its
      * bio_lists[] and decrease total number queued.  The caller is
      * responsible for issuing these bios.
      */
     if (parent_tg) {
         throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
         start_parent_slice_with_credit(tg, parent_tg, rw);
     } else {
         throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
                      &parent_sq->queued[rw]);
         BUG_ON(tg->td->nr_queued[rw] <= 0);
         tg->td->nr_queued[rw]--;
     }
 
     throtl_trim_slice(tg, rw);
 
     if (tg_to_put)
         blkg_put(tg_to_blkg(tg_to_put));
 }
 
 static int throtl_dispatch_tg(struct throtl_grp *tg)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     unsigned int nr_reads = 0, nr_writes = 0;
     unsigned int max_nr_reads = THROTL_GRP_QUANTUM * 3 / 4;
     unsigned int max_nr_writes = THROTL_GRP_QUANTUM - max_nr_reads;
     struct bio *bio;
 
     /* Try to dispatch 75% READS and 25% WRITES */
 
     while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
            tg_may_dispatch(tg, bio, NULL)) {
 
         tg_dispatch_one_bio(tg, bio_data_dir(bio));
         nr_reads++;
 
         if (nr_reads >= max_nr_reads)
             break;
     }
 
     while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
            tg_may_dispatch(tg, bio, NULL)) {
 
         tg_dispatch_one_bio(tg, bio_data_dir(bio));
         nr_writes++;
 
         if (nr_writes >= max_nr_writes)
             break;
     }
 
     return nr_reads + nr_writes;
 }
 
 static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 {
     unsigned int nr_disp = 0;
 
     while (1) {
         struct throtl_grp *tg;
         struct throtl_service_queue *sq;
 
         if (!parent_sq->nr_pending)
             break;
 
         tg = throtl_rb_first(parent_sq);
         if (!tg)
             break;
 
         if (time_before(jiffies, tg->disptime))
             break;
 
         throtl_dequeue_tg(tg);
 
         nr_disp += throtl_dispatch_tg(tg);
 
         sq = &tg->service_queue;
         if (sq->nr_queued[0] || sq->nr_queued[1])
             tg_update_disptime(tg);
 
         if (nr_disp >= THROTL_QUANTUM)
             break;
     }
 
     return nr_disp;
 }
 
 static bool throtl_can_upgrade(struct throtl_data *td,
     struct throtl_grp *this_tg);
 /**
  * throtl_pending_timer_fn - timer function for service_queue->pending_timer
  * @t: the pending_timer member of the throtl_service_queue being serviced
  *
  * This timer is armed when a child throtl_grp with active bio's become
  * pending and queued on the service_queue's pending_tree and expires when
  * the first child throtl_grp should be dispatched.  This function
  * dispatches bio's from the children throtl_grps to the parent
  * service_queue.
  *
  * If the parent's parent is another throtl_grp, dispatching is propagated
  * by either arming its pending_timer or repeating dispatch directly.  If
  * the top-level service_tree is reached, throtl_data->dispatch_work is
  * kicked so that the ready bio's are issued.
  */
 static void throtl_pending_timer_fn(struct timer_list *t)
 {
     struct throtl_service_queue *sq = from_timer(sq, t, pending_timer);
     struct throtl_grp *tg = sq_to_tg(sq);
     struct throtl_data *td = sq_to_td(sq);
     struct throtl_service_queue *parent_sq;
     struct request_queue *q;
     bool dispatched;
     int ret;
 
     /* throtl_data may be gone, so figure out request queue by blkg */
     if (tg)
         q = tg->pd.blkg->q;
     else
         q = td->queue;
 
     spin_lock_irq(&q->queue_lock);
 
     if (!q->root_blkg)
         goto out_unlock;
 
     if (throtl_can_upgrade(td, NULL))
         throtl_upgrade_state(td);
 
 again:
     parent_sq = sq->parent_sq;
     dispatched = false;
 
     while (true) {
         throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
                sq->nr_queued[READ] + sq->nr_queued[WRITE],
                sq->nr_queued[READ], sq->nr_queued[WRITE]);
 
         ret = throtl_select_dispatch(sq);
         if (ret) {
             throtl_log(sq, "bios disp=%u", ret);
             dispatched = true;
         }
 
         if (throtl_schedule_next_dispatch(sq, false))
             break;
 
         /* this dispatch windows is still open, relax and repeat */
         spin_unlock_irq(&q->queue_lock);
         cpu_relax();
         spin_lock_irq(&q->queue_lock);
     }
 
     if (!dispatched)
         goto out_unlock;
 
     if (parent_sq) {
         /* @parent_sq is another throl_grp, propagate dispatch */
         if (tg->flags & THROTL_TG_WAS_EMPTY) {
             tg_update_disptime(tg);
             if (!throtl_schedule_next_dispatch(parent_sq, false)) {
                 /* window is already open, repeat dispatching */
                 sq = parent_sq;
                 tg = sq_to_tg(sq);
                 goto again;
             }
         }
     } else {
         /* reached the top-level, queue issuing */
         queue_work(kthrotld_workqueue, &td->dispatch_work);
     }
 out_unlock:
     spin_unlock_irq(&q->queue_lock);
 }
 
 /**
  * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
  * @work: work item being executed
  *
  * This function is queued for execution when bios reach the bio_lists[]
  * of throtl_data->service_queue.  Those bios are ready and issued by this
  * function.
  */
 static void blk_throtl_dispatch_work_fn(struct work_struct *work)
 {
     struct throtl_data *td = container_of(work, struct throtl_data,
                           dispatch_work);
     struct throtl_service_queue *td_sq = &td->service_queue;
     struct request_queue *q = td->queue;
     struct bio_list bio_list_on_stack;
     struct bio *bio;
     struct blk_plug plug;
     int rw;
 
     bio_list_init(&bio_list_on_stack);
 
     spin_lock_irq(&q->queue_lock);
     for (rw = READ; rw <= WRITE; rw++)
         while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
             bio_list_add(&bio_list_on_stack, bio);
     spin_unlock_irq(&q->queue_lock);
 
     if (!bio_list_empty(&bio_list_on_stack)) {
         blk_start_plug(&plug);
         while ((bio = bio_list_pop(&bio_list_on_stack)))
             submit_bio_noacct_nocheck(bio);
         blk_finish_plug(&plug);
     }
 }
 
 static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
                   int off)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
     u64 v = *(u64 *)((void *)tg + off);
 
     if (v == U64_MAX)
         return 0;
     return __blkg_prfill_u64(sf, pd, v);
 }
 
 static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
                    int off)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
     unsigned int v = *(unsigned int *)((void *)tg + off);
 
     if (v == UINT_MAX)
         return 0;
     return __blkg_prfill_u64(sf, pd, v);
 }
 
 static int tg_print_conf_u64(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
               &blkcg_policy_throtl, seq_cft(sf)->private, false);
     return 0;
 }
 
 static int tg_print_conf_uint(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
               &blkcg_policy_throtl, seq_cft(sf)->private, false);
     return 0;
 }
 
 static void tg_conf_updated(struct throtl_grp *tg, bool global)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     struct cgroup_subsys_state *pos_css;
     struct blkcg_gq *blkg;
 
     throtl_log(&tg->service_queue,
            "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
            tg_bps_limit(tg, READ), tg_bps_limit(tg, WRITE),
            tg_iops_limit(tg, READ), tg_iops_limit(tg, WRITE));
 
     /*
      * Update has_rules[] flags for the updated tg's subtree.  A tg is
      * considered to have rules if either the tg itself or any of its
      * ancestors has rules.  This identifies groups without any
      * restrictions in the whole hierarchy and allows them to bypass
      * blk-throttle.
      */
     blkg_for_each_descendant_pre(blkg, pos_css,
             global ? tg->td->queue->root_blkg : tg_to_blkg(tg)) {
         struct throtl_grp *this_tg = blkg_to_tg(blkg);
         struct throtl_grp *parent_tg;
 
         tg_update_has_rules(this_tg);
         /* ignore root/second level */
         if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent ||
             !blkg->parent->parent)
             continue;
         parent_tg = blkg_to_tg(blkg->parent);
         /*
          * make sure all children has lower idle time threshold and
          * higher latency target
          */
         this_tg->idletime_threshold = min(this_tg->idletime_threshold,
                 parent_tg->idletime_threshold);
         this_tg->latency_target = max(this_tg->latency_target,
                 parent_tg->latency_target);
     }
 
     /*
      * We're already holding queue_lock and know @tg is valid.  Let's
      * apply the new config directly.
      *
      * Restart the slices for both READ and WRITES. It might happen
      * that a group's limit are dropped suddenly and we don't want to
      * account recently dispatched IO with new low rate.
      */
     throtl_start_new_slice(tg, READ);
     throtl_start_new_slice(tg, WRITE);
 
     if (tg->flags & THROTL_TG_PENDING) {
         tg_update_disptime(tg);
         throtl_schedule_next_dispatch(sq->parent_sq, true);
     }
 }
 
 static ssize_t tg_set_conf(struct kernfs_open_file *of,
                char *buf, size_t nbytes, loff_t off, bool is_u64)
 {
     struct blkcg *blkcg = css_to_blkcg(of_css(of));
     struct blkg_conf_ctx ctx;
     struct throtl_grp *tg;
     int ret;
     u64 v;
 
     ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
     if (ret)
         return ret;
 
     ret = -EINVAL;
     if (sscanf(ctx.body, "%llu", &v) != 1)
         goto out_finish;
     if (!v)
         v = U64_MAX;
 
     tg = blkg_to_tg(ctx.blkg);
 
     if (is_u64)
         *(u64 *)((void *)tg + of_cft(of)->private) = v;
     else
         *(unsigned int *)((void *)tg + of_cft(of)->private) = v;
 
     tg_conf_updated(tg, false);
     ret = 0;
 out_finish:
     blkg_conf_finish(&ctx);
     return ret ?: nbytes;
 }
 
 static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
                    char *buf, size_t nbytes, loff_t off)
 {
     return tg_set_conf(of, buf, nbytes, off, true);
 }
 
 static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
                 char *buf, size_t nbytes, loff_t off)
 {
     return tg_set_conf(of, buf, nbytes, off, false);
 }
 
 static int tg_print_rwstat(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
               blkg_prfill_rwstat, &blkcg_policy_throtl,
               seq_cft(sf)->private, true);
     return 0;
 }
 
 static u64 tg_prfill_rwstat_recursive(struct seq_file *sf,
                       struct blkg_policy_data *pd, int off)
 {
     struct blkg_rwstat_sample sum;
 
     blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_throtl, off,
                   &sum);
     return __blkg_prfill_rwstat(sf, pd, &sum);
 }
 
 static int tg_print_rwstat_recursive(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
               tg_prfill_rwstat_recursive, &blkcg_policy_throtl,
               seq_cft(sf)->private, true);
     return 0;
 }
 
 static struct cftype throtl_legacy_files[] = {
     {
         .name = "throttle.read_bps_device",
         .private = offsetof(struct throtl_grp, bps[READ][LIMIT_MAX]),
         .seq_show = tg_print_conf_u64,
         .write = tg_set_conf_u64,
     },
     {
         .name = "throttle.write_bps_device",
         .private = offsetof(struct throtl_grp, bps[WRITE][LIMIT_MAX]),
         .seq_show = tg_print_conf_u64,
         .write = tg_set_conf_u64,
     },
     {
         .name = "throttle.read_iops_device",
         .private = offsetof(struct throtl_grp, iops[READ][LIMIT_MAX]),
         .seq_show = tg_print_conf_uint,
         .write = tg_set_conf_uint,
     },
     {
         .name = "throttle.write_iops_device",
         .private = offsetof(struct throtl_grp, iops[WRITE][LIMIT_MAX]),
         .seq_show = tg_print_conf_uint,
         .write = tg_set_conf_uint,
     },
     {
         .name = "throttle.io_service_bytes",
         .private = offsetof(struct throtl_grp, stat_bytes),
         .seq_show = tg_print_rwstat,
     },
     {
         .name = "throttle.io_service_bytes_recursive",
         .private = offsetof(struct throtl_grp, stat_bytes),
         .seq_show = tg_print_rwstat_recursive,
     },
     {
         .name = "throttle.io_serviced",
         .private = offsetof(struct throtl_grp, stat_ios),
         .seq_show = tg_print_rwstat,
     },
     {
         .name = "throttle.io_serviced_recursive",
         .private = offsetof(struct throtl_grp, stat_ios),
         .seq_show = tg_print_rwstat_recursive,
     },
     { } /* terminate */
 };
 
 static u64 tg_prfill_limit(struct seq_file *sf, struct blkg_policy_data *pd,
              int off)
 {
     struct throtl_grp *tg = pd_to_tg(pd);
     const char *dname = blkg_dev_name(pd->blkg);
     char bufs[4][21] = { "max", "max", "max", "max" };
     u64 bps_dft;
     unsigned int iops_dft;
     char idle_time[26] = "";
     char latency_time[26] = "";
 
     if (!dname)
         return 0;
 
     if (off == LIMIT_LOW) {
         bps_dft = 0;
         iops_dft = 0;
     } else {
         bps_dft = U64_MAX;
         iops_dft = UINT_MAX;
     }
 
     if (tg->bps_conf[READ][off] == bps_dft &&
         tg->bps_conf[WRITE][off] == bps_dft &&
         tg->iops_conf[READ][off] == iops_dft &&
         tg->iops_conf[WRITE][off] == iops_dft &&
         (off != LIMIT_LOW ||
          (tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD &&
           tg->latency_target_conf == DFL_LATENCY_TARGET)))
         return 0;
 
     if (tg->bps_conf[READ][off] != U64_MAX)
         snprintf(bufs[0], sizeof(bufs[0]), "%llu",
             tg->bps_conf[READ][off]);
     if (tg->bps_conf[WRITE][off] != U64_MAX)
         snprintf(bufs[1], sizeof(bufs[1]), "%llu",
             tg->bps_conf[WRITE][off]);
     if (tg->iops_conf[READ][off] != UINT_MAX)
         snprintf(bufs[2], sizeof(bufs[2]), "%u",
             tg->iops_conf[READ][off]);
     if (tg->iops_conf[WRITE][off] != UINT_MAX)
         snprintf(bufs[3], sizeof(bufs[3]), "%u",
             tg->iops_conf[WRITE][off]);
     if (off == LIMIT_LOW) {
         if (tg->idletime_threshold_conf == ULONG_MAX)
             strcpy(idle_time, " idle=max");
         else
             snprintf(idle_time, sizeof(idle_time), " idle=%lu",
                 tg->idletime_threshold_conf);
 
         if (tg->latency_target_conf == ULONG_MAX)
             strcpy(latency_time, " latency=max");
         else
             snprintf(latency_time, sizeof(latency_time),
                 " latency=%lu", tg->latency_target_conf);
     }
 
     seq_printf(sf, "%s rbps=%s wbps=%s riops=%s wiops=%s%s%s\n",
            dname, bufs[0], bufs[1], bufs[2], bufs[3], idle_time,
            latency_time);
     return 0;
 }
 
 static int tg_print_limit(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_limit,
               &blkcg_policy_throtl, seq_cft(sf)->private, false);
     return 0;
 }
 
 static ssize_t tg_set_limit(struct kernfs_open_file *of,
               char *buf, size_t nbytes, loff_t off)
 {
     struct blkcg *blkcg = css_to_blkcg(of_css(of));
     struct blkg_conf_ctx ctx;
     struct throtl_grp *tg;
     u64 v[4];
     unsigned long idle_time;
     unsigned long latency_time;
     int ret;
     int index = of_cft(of)->private;
 
     ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
     if (ret)
         return ret;
 
     tg = blkg_to_tg(ctx.blkg);
 
     v[0] = tg->bps_conf[READ][index];
     v[1] = tg->bps_conf[WRITE][index];
     v[2] = tg->iops_conf[READ][index];
     v[3] = tg->iops_conf[WRITE][index];
 
     idle_time = tg->idletime_threshold_conf;
     latency_time = tg->latency_target_conf;
     while (true) {
         char tok[27];   /* wiops=18446744073709551616 */
         char *p;
         u64 val = U64_MAX;
         int len;
 
         if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
             break;
         if (tok[0] == '\0')
             break;
         ctx.body += len;
 
         ret = -EINVAL;
         p = tok;
         strsep(&p, "=");
         if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
             goto out_finish;
 
         ret = -ERANGE;
         if (!val)
             goto out_finish;
 
         ret = -EINVAL;
         if (!strcmp(tok, "rbps") && val > 1)
             v[0] = val;
         else if (!strcmp(tok, "wbps") && val > 1)
             v[1] = val;
         else if (!strcmp(tok, "riops") && val > 1)
             v[2] = min_t(u64, val, UINT_MAX);
         else if (!strcmp(tok, "wiops") && val > 1)
             v[3] = min_t(u64, val, UINT_MAX);
         else if (off == LIMIT_LOW && !strcmp(tok, "idle"))
             idle_time = val;
         else if (off == LIMIT_LOW && !strcmp(tok, "latency"))
             latency_time = val;
         else
             goto out_finish;
     }
 
     tg->bps_conf[READ][index] = v[0];
     tg->bps_conf[WRITE][index] = v[1];
     tg->iops_conf[READ][index] = v[2];
     tg->iops_conf[WRITE][index] = v[3];
 
     if (index == LIMIT_MAX) {
         tg->bps[READ][index] = v[0];
         tg->bps[WRITE][index] = v[1];
         tg->iops[READ][index] = v[2];
         tg->iops[WRITE][index] = v[3];
     }
     tg->bps[READ][LIMIT_LOW] = min(tg->bps_conf[READ][LIMIT_LOW],
         tg->bps_conf[READ][LIMIT_MAX]);
     tg->bps[WRITE][LIMIT_LOW] = min(tg->bps_conf[WRITE][LIMIT_LOW],
         tg->bps_conf[WRITE][LIMIT_MAX]);
     tg->iops[READ][LIMIT_LOW] = min(tg->iops_conf[READ][LIMIT_LOW],
         tg->iops_conf[READ][LIMIT_MAX]);
     tg->iops[WRITE][LIMIT_LOW] = min(tg->iops_conf[WRITE][LIMIT_LOW],
         tg->iops_conf[WRITE][LIMIT_MAX]);
     tg->idletime_threshold_conf = idle_time;
     tg->latency_target_conf = latency_time;
 
     /* force user to configure all settings for low limit  */
     if (!(tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW] ||
           tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) ||
         tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD ||
         tg->latency_target_conf == DFL_LATENCY_TARGET) {
         tg->bps[READ][LIMIT_LOW] = 0;
         tg->bps[WRITE][LIMIT_LOW] = 0;
         tg->iops[READ][LIMIT_LOW] = 0;
         tg->iops[WRITE][LIMIT_LOW] = 0;
         tg->idletime_threshold = DFL_IDLE_THRESHOLD;
         tg->latency_target = DFL_LATENCY_TARGET;
     } else if (index == LIMIT_LOW) {
         tg->idletime_threshold = tg->idletime_threshold_conf;
         tg->latency_target = tg->latency_target_conf;
     }
 
     blk_throtl_update_limit_valid(tg->td);
     if (tg->td->limit_valid[LIMIT_LOW]) {
         if (index == LIMIT_LOW)
             tg->td->limit_index = LIMIT_LOW;
     } else
         tg->td->limit_index = LIMIT_MAX;
     tg_conf_updated(tg, index == LIMIT_LOW &&
         tg->td->limit_valid[LIMIT_LOW]);
     ret = 0;
 out_finish:
     blkg_conf_finish(&ctx);
     return ret ?: nbytes;
 }
 
 static struct cftype throtl_files[] = {
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
     {
         .name = "low",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = tg_print_limit,
         .write = tg_set_limit,
         .private = LIMIT_LOW,
     },
 #endif
     {
         .name = "max",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = tg_print_limit,
         .write = tg_set_limit,
         .private = LIMIT_MAX,
     },
     { } /* terminate */
 };
 
 static void throtl_shutdown_wq(struct request_queue *q)
 {
     struct throtl_data *td = q->td;
 
     cancel_work_sync(&td->dispatch_work);
 }
 
 struct blkcg_policy blkcg_policy_throtl = {
     .dfl_cftypes        = throtl_files,
     .legacy_cftypes     = throtl_legacy_files,
 
     .pd_alloc_fn        = throtl_pd_alloc,
     .pd_init_fn     = throtl_pd_init,
     .pd_online_fn       = throtl_pd_online,
     .pd_offline_fn      = throtl_pd_offline,
     .pd_free_fn     = throtl_pd_free,
 };
 
 static unsigned long __tg_last_low_overflow_time(struct throtl_grp *tg)
 {
     unsigned long rtime = jiffies, wtime = jiffies;
 
     if (tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW])
         rtime = tg->last_low_overflow_time[READ];
     if (tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
         wtime = tg->last_low_overflow_time[WRITE];
     return min(rtime, wtime);
 }
 
 /* tg should not be an intermediate node */
 static unsigned long tg_last_low_overflow_time(struct throtl_grp *tg)
 {
     struct throtl_service_queue *parent_sq;
     struct throtl_grp *parent = tg;
     unsigned long ret = __tg_last_low_overflow_time(tg);
 
     while (true) {
         parent_sq = parent->service_queue.parent_sq;
         parent = sq_to_tg(parent_sq);
         if (!parent)
             break;
 
         /*
          * The parent doesn't have low limit, it always reaches low
          * limit. Its overflow time is useless for children
          */
         if (!parent->bps[READ][LIMIT_LOW] &&
             !parent->iops[READ][LIMIT_LOW] &&
             !parent->bps[WRITE][LIMIT_LOW] &&
             !parent->iops[WRITE][LIMIT_LOW])
             continue;
         if (time_after(__tg_last_low_overflow_time(parent), ret))
             ret = __tg_last_low_overflow_time(parent);
     }
     return ret;
 }
 
 static bool throtl_tg_is_idle(struct throtl_grp *tg)
 {
     /*
      * cgroup is idle if:
      * - single idle is too long, longer than a fixed value (in case user
      *   configure a too big threshold) or 4 times of idletime threshold
      * - average think time is more than threshold
      * - IO latency is largely below threshold
      */
     unsigned long time;
     bool ret;
 
     time = min_t(unsigned long, MAX_IDLE_TIME, 4 * tg->idletime_threshold);
     ret = tg->latency_target == DFL_LATENCY_TARGET ||
           tg->idletime_threshold == DFL_IDLE_THRESHOLD ||
           (ktime_get_ns() >> 10) - tg->last_finish_time > time ||
           tg->avg_idletime > tg->idletime_threshold ||
           (tg->latency_target && tg->bio_cnt &&
         tg->bad_bio_cnt * 5 < tg->bio_cnt);
     throtl_log(&tg->service_queue,
         "avg_idle=%ld, idle_threshold=%ld, bad_bio=%d, total_bio=%d, is_idle=%d, scale=%d",
         tg->avg_idletime, tg->idletime_threshold, tg->bad_bio_cnt,
         tg->bio_cnt, ret, tg->td->scale);
     return ret;
 }
 
 static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
 {
     struct throtl_service_queue *sq = &tg->service_queue;
     bool read_limit, write_limit;
 
     /*
      * if cgroup reaches low limit (if low limit is 0, the cgroup always
      * reaches), it's ok to upgrade to next limit
      */
     read_limit = tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW];
     write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
     if (!read_limit && !write_limit)
         return true;
     if (read_limit && sq->nr_queued[READ] &&
         (!write_limit || sq->nr_queued[WRITE]))
         return true;
     if (write_limit && sq->nr_queued[WRITE] &&
         (!read_limit || sq->nr_queued[READ]))
         return true;
 
     if (time_after_eq(jiffies,
         tg_last_low_overflow_time(tg) + tg->td->throtl_slice) &&
         throtl_tg_is_idle(tg))
         return true;
     return false;
 }
 
 static bool throtl_hierarchy_can_upgrade(struct throtl_grp *tg)
 {
     while (true) {
         if (throtl_tg_can_upgrade(tg))
             return true;
         tg = sq_to_tg(tg->service_queue.parent_sq);
         if (!tg || !tg_to_blkg(tg)->parent)
             return false;
     }
     return false;
 }
 
 void blk_throtl_cancel_bios(struct request_queue *q)
 {
     struct cgroup_subsys_state *pos_css;
     struct blkcg_gq *blkg;
 
     spin_lock_irq(&q->queue_lock);
     /*
      * queue_lock is held, rcu lock is not needed here technically.
      * However, rcu lock is still held to emphasize that following
      * path need RCU protection and to prevent warning from lockdep.
      */
     rcu_read_lock();
     blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg) {
         struct throtl_grp *tg = blkg_to_tg(blkg);
         struct throtl_service_queue *sq = &tg->service_queue;
 
         /*
          * Set the flag to make sure throtl_pending_timer_fn() won't
          * stop until all throttled bios are dispatched.
          */
         blkg_to_tg(blkg)->flags |= THROTL_TG_CANCELING;
         /*
          * Update disptime after setting the above flag to make sure
          * throtl_select_dispatch() won't exit without dispatching.
          */
         tg_update_disptime(tg);
 
         throtl_schedule_pending_timer(sq, jiffies + 1);
     }
     rcu_read_unlock();
     spin_unlock_irq(&q->queue_lock);
 }
 
 static bool throtl_can_upgrade(struct throtl_data *td,
     struct throtl_grp *this_tg)
 {
     struct cgroup_subsys_state *pos_css;
     struct blkcg_gq *blkg;
 
     if (td->limit_index != LIMIT_LOW)
         return false;
 
     if (time_before(jiffies, td->low_downgrade_time + td->throtl_slice))
         return false;
 
     rcu_read_lock();
     blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
         struct throtl_grp *tg = blkg_to_tg(blkg);
 
         if (tg == this_tg)
             continue;
         if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
             continue;
         if (!throtl_hierarchy_can_upgrade(tg)) {
             rcu_read_unlock();
             return false;
         }
     }
     rcu_read_unlock();
     return true;
 }
 
 static void throtl_upgrade_check(struct throtl_grp *tg)
 {
     unsigned long now = jiffies;
 
     if (tg->td->limit_index != LIMIT_LOW)
         return;
 
     if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
         return;
 
     tg->last_check_time = now;
 
     if (!time_after_eq(now,
          __tg_last_low_overflow_time(tg) + tg->td->throtl_slice))
         return;
 
     if (throtl_can_upgrade(tg->td, NULL))
         throtl_upgrade_state(tg->td);
 }
 
 static void throtl_upgrade_state(struct throtl_data *td)
 {
     struct cgroup_subsys_state *pos_css;
     struct blkcg_gq *blkg;
 
     throtl_log(&td->service_queue, "upgrade to max");
     td->limit_index = LIMIT_MAX;
     td->low_upgrade_time = jiffies;
     td->scale = 0;
     rcu_read_lock();
     blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
         struct throtl_grp *tg = blkg_to_tg(blkg);
         struct throtl_service_queue *sq = &tg->service_queue;
 
         tg->disptime = jiffies - 1;
         throtl_select_dispatch(sq);
         throtl_schedule_next_dispatch(sq, true);
     }
     rcu_read_unlock();
     throtl_select_dispatch(&td->service_queue);
     throtl_schedule_next_dispatch(&td->service_queue, true);
     queue_work(kthrotld_workqueue, &td->dispatch_work);
 }
 
 static void throtl_downgrade_state(struct throtl_data *td)
 {
     td->scale /= 2;
 
     throtl_log(&td->service_queue, "downgrade, scale %d", td->scale);
     if (td->scale) {
         td->low_upgrade_time = jiffies - td->scale * td->throtl_slice;
         return;
     }
 
     td->limit_index = LIMIT_LOW;
     td->low_downgrade_time = jiffies;
 }
 
 static bool throtl_tg_can_downgrade(struct throtl_grp *tg)
 {
     struct throtl_data *td = tg->td;
     unsigned long now = jiffies;
 
     /*
      * If cgroup is below low limit, consider downgrade and throttle other
      * cgroups
      */
     if (time_after_eq(now, td->low_upgrade_time + td->throtl_slice) &&
         time_after_eq(now, tg_last_low_overflow_time(tg) +
                     td->throtl_slice) &&
         (!throtl_tg_is_idle(tg) ||
          !list_empty(&tg_to_blkg(tg)->blkcg->css.children)))
         return true;
     return false;
 }
 
 static bool throtl_hierarchy_can_downgrade(struct throtl_grp *tg)
 {
     while (true) {
         if (!throtl_tg_can_downgrade(tg))
             return false;
         tg = sq_to_tg(tg->service_queue.parent_sq);
         if (!tg || !tg_to_blkg(tg)->parent)
             break;
     }
     return true;
 }
 
 static void throtl_downgrade_check(struct throtl_grp *tg)
 {
     uint64_t bps;
     unsigned int iops;
     unsigned long elapsed_time;
     unsigned long now = jiffies;
 
     if (tg->td->limit_index != LIMIT_MAX ||
         !tg->td->limit_valid[LIMIT_LOW])
         return;
     if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
         return;
     if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
         return;
 
     elapsed_time = now - tg->last_check_time;
     tg->last_check_time = now;
 
     if (time_before(now, tg_last_low_overflow_time(tg) +
             tg->td->throtl_slice))
         return;
 
     if (tg->bps[READ][LIMIT_LOW]) {
         bps = tg->last_bytes_disp[READ] * HZ;
         do_div(bps, elapsed_time);
         if (bps >= tg->bps[READ][LIMIT_LOW])
             tg->last_low_overflow_time[READ] = now;
     }
 
     if (tg->bps[WRITE][LIMIT_LOW]) {
         bps = tg->last_bytes_disp[WRITE] * HZ;
         do_div(bps, elapsed_time);
         if (bps >= tg->bps[WRITE][LIMIT_LOW])
             tg->last_low_overflow_time[WRITE] = now;
     }
 
     if (tg->iops[READ][LIMIT_LOW]) {
         iops = tg->last_io_disp[READ] * HZ / elapsed_time;
         if (iops >= tg->iops[READ][LIMIT_LOW])
             tg->last_low_overflow_time[READ] = now;
     }
 
     if (tg->iops[WRITE][LIMIT_LOW]) {
         iops = tg->last_io_disp[WRITE] * HZ / elapsed_time;
         if (iops >= tg->iops[WRITE][LIMIT_LOW])
             tg->last_low_overflow_time[WRITE] = now;
     }
 
     /*
      * If cgroup is below low limit, consider downgrade and throttle other
      * cgroups
      */
     if (throtl_hierarchy_can_downgrade(tg))
         throtl_downgrade_state(tg->td);
 
     tg->last_bytes_disp[READ] = 0;
     tg->last_bytes_disp[WRITE] = 0;
     tg->last_io_disp[READ] = 0;
     tg->last_io_disp[WRITE] = 0;
 }
 
 static void blk_throtl_update_idletime(struct throtl_grp *tg)
 {
     unsigned long now;
     unsigned long last_finish_time = tg->last_finish_time;
 
     if (last_finish_time == 0)
         return;
 
     now = ktime_get_ns() >> 10;
     if (now <= last_finish_time ||
         last_finish_time == tg->checked_last_finish_time)
         return;
 
     tg->avg_idletime = (tg->avg_idletime * 7 + now - last_finish_time) >> 3;
     tg->checked_last_finish_time = last_finish_time;
 }
 
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 static void throtl_update_latency_buckets(struct throtl_data *td)
 {
     struct avg_latency_bucket avg_latency[2][LATENCY_BUCKET_SIZE];
     int i, cpu, rw;
     unsigned long last_latency[2] = { 0 };
     unsigned long latency[2];
 
     if (!blk_queue_nonrot(td->queue) || !td->limit_valid[LIMIT_LOW])
         return;
     if (time_before(jiffies, td->last_calculate_time + HZ))
         return;
     td->last_calculate_time = jiffies;
 
     memset(avg_latency, 0, sizeof(avg_latency));
     for (rw = READ; rw <= WRITE; rw++) {
         for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
             struct latency_bucket *tmp = &td->tmp_buckets[rw][i];
 
             for_each_possible_cpu(cpu) {
                 struct latency_bucket *bucket;
 
                 /* this isn't race free, but ok in practice */
                 bucket = per_cpu_ptr(td->latency_buckets[rw],
                     cpu);
                 tmp->total_latency += bucket[i].total_latency;
                 tmp->samples += bucket[i].samples;
                 bucket[i].total_latency = 0;
                 bucket[i].samples = 0;
             }
 
             if (tmp->samples >= 32) {
                 int samples = tmp->samples;
 
                 latency[rw] = tmp->total_latency;
 
                 tmp->total_latency = 0;
                 tmp->samples = 0;
                 latency[rw] /= samples;
                 if (latency[rw] == 0)
                     continue;
                 avg_latency[rw][i].latency = latency[rw];
             }
         }
     }
 
     for (rw = READ; rw <= WRITE; rw++) {
         for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
             if (!avg_latency[rw][i].latency) {
                 if (td->avg_buckets[rw][i].latency < last_latency[rw])
                     td->avg_buckets[rw][i].latency =
                         last_latency[rw];
                 continue;
             }
 
             if (!td->avg_buckets[rw][i].valid)
                 latency[rw] = avg_latency[rw][i].latency;
             else
                 latency[rw] = (td->avg_buckets[rw][i].latency * 7 +
                     avg_latency[rw][i].latency) >> 3;
 
             td->avg_buckets[rw][i].latency = max(latency[rw],
                 last_latency[rw]);
             td->avg_buckets[rw][i].valid = true;
             last_latency[rw] = td->avg_buckets[rw][i].latency;
         }
     }
 
     for (i = 0; i < LATENCY_BUCKET_SIZE; i++)
         throtl_log(&td->service_queue,
             "Latency bucket %d: read latency=%ld, read valid=%d, "
             "write latency=%ld, write valid=%d", i,
             td->avg_buckets[READ][i].latency,
             td->avg_buckets[READ][i].valid,
             td->avg_buckets[WRITE][i].latency,
             td->avg_buckets[WRITE][i].valid);
 }
 #else
 static inline void throtl_update_latency_buckets(struct throtl_data *td)
 {
 }
 #endif
 
 bool __blk_throtl_bio(struct bio *bio)
 {
     struct request_queue *q = bdev_get_queue(bio->bi_bdev);
     struct blkcg_gq *blkg = bio->bi_blkg;
     struct throtl_qnode *qn = NULL;
     struct throtl_grp *tg = blkg_to_tg(blkg);
     struct throtl_service_queue *sq;
     bool rw = bio_data_dir(bio);
     bool throttled = false;
     struct throtl_data *td = tg->td;
 
     rcu_read_lock();
 
     if (!cgroup_subsys_on_dfl(io_cgrp_subsys)) {
         blkg_rwstat_add(&tg->stat_bytes, bio->bi_opf,
                 bio->bi_iter.bi_size);
         blkg_rwstat_add(&tg->stat_ios, bio->bi_opf, 1);
     }
 
     spin_lock_irq(&q->queue_lock);
 
     throtl_update_latency_buckets(td);
 
     blk_throtl_update_idletime(tg);
 
     sq = &tg->service_queue;
 
 again:
     while (true) {
         if (tg->last_low_overflow_time[rw] == 0)
             tg->last_low_overflow_time[rw] = jiffies;
         throtl_downgrade_check(tg);
         throtl_upgrade_check(tg);
         /* throtl is FIFO - if bios are already queued, should queue */
         if (sq->nr_queued[rw])
             break;
 
         /* if above limits, break to queue */
         if (!tg_may_dispatch(tg, bio, NULL)) {
             tg->last_low_overflow_time[rw] = jiffies;
             if (throtl_can_upgrade(td, tg)) {
                 throtl_upgrade_state(td);
                 goto again;
             }
             break;
         }
 
         /* within limits, let's charge and dispatch directly */
         throtl_charge_bio(tg, bio);
 
         /*
          * We need to trim slice even when bios are not being queued
          * otherwise it might happen that a bio is not queued for
          * a long time and slice keeps on extending and trim is not
          * called for a long time. Now if limits are reduced suddenly
          * we take into account all the IO dispatched so far at new
          * low rate and * newly queued IO gets a really long dispatch
          * time.
          *
          * So keep on trimming slice even if bio is not queued.
          */
         throtl_trim_slice(tg, rw);
 
         /*
          * @bio passed through this layer without being throttled.
          * Climb up the ladder.  If we're already at the top, it
          * can be executed directly.
          */
         qn = &tg->qnode_on_parent[rw];
         sq = sq->parent_sq;
         tg = sq_to_tg(sq);
         if (!tg)
             goto out_unlock;
     }
 
     /* out-of-limit, queue to @tg */
     throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
            rw == READ ? 'R' : 'W',
            tg->bytes_disp[rw], bio->bi_iter.bi_size,
            tg_bps_limit(tg, rw),
            tg->io_disp[rw], tg_iops_limit(tg, rw),
            sq->nr_queued[READ], sq->nr_queued[WRITE]);
 
     tg->last_low_overflow_time[rw] = jiffies;
 
     td->nr_queued[rw]++;
     throtl_add_bio_tg(bio, qn, tg);
     throttled = true;
 
     /*
      * Update @tg's dispatch time and force schedule dispatch if @tg
      * was empty before @bio.  The forced scheduling isn't likely to
      * cause undue delay as @bio is likely to be dispatched directly if
      * its @tg's disptime is not in the future.
      */
     if (tg->flags & THROTL_TG_WAS_EMPTY) {
         tg_update_disptime(tg);
         throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
     }
 
 out_unlock:
     bio_set_flag(bio, BIO_THROTTLED);
 
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
     if (throttled || !td->track_bio_latency)
         bio->bi_issue.value |= BIO_ISSUE_THROTL_SKIP_LATENCY;
 #endif
     spin_unlock_irq(&q->queue_lock);
 
     rcu_read_unlock();
     return throttled;
 }
 
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 static void throtl_track_latency(struct throtl_data *td, sector_t size,
                  enum req_op op, unsigned long time)
 {
     const bool rw = op_is_write(op);
     struct latency_bucket *latency;
     int index;
 
     if (!td || td->limit_index != LIMIT_LOW ||
         !(op == REQ_OP_READ || op == REQ_OP_WRITE) ||
         !blk_queue_nonrot(td->queue))
         return;
 
     index = request_bucket_index(size);
 
     latency = get_cpu_ptr(td->latency_buckets[rw]);
     latency[index].total_latency += time;
     latency[index].samples++;
     put_cpu_ptr(td->latency_buckets[rw]);
 }
 
 void blk_throtl_stat_add(struct request *rq, u64 time_ns)
 {
     struct request_queue *q = rq->q;
     struct throtl_data *td = q->td;
 
     throtl_track_latency(td, blk_rq_stats_sectors(rq), req_op(rq),
                  time_ns >> 10);
 }
 
 void blk_throtl_bio_endio(struct bio *bio)
 {
     struct blkcg_gq *blkg;
     struct throtl_grp *tg;
     u64 finish_time_ns;
     unsigned long finish_time;
     unsigned long start_time;
     unsigned long lat;
     int rw = bio_data_dir(bio);
 
     blkg = bio->bi_blkg;
     if (!blkg)
         return;
     tg = blkg_to_tg(blkg);
     if (!tg->td->limit_valid[LIMIT_LOW])
         return;
 
     finish_time_ns = ktime_get_ns();
     tg->last_finish_time = finish_time_ns >> 10;
 
     start_time = bio_issue_time(&bio->bi_issue) >> 10;
     finish_time = __bio_issue_time(finish_time_ns) >> 10;
     if (!start_time || finish_time <= start_time)
         return;
 
     lat = finish_time - start_time;
     /* this is only for bio based driver */
     if (!(bio->bi_issue.value & BIO_ISSUE_THROTL_SKIP_LATENCY))
         throtl_track_latency(tg->td, bio_issue_size(&bio->bi_issue),
                      bio_op(bio), lat);
 
     if (tg->latency_target && lat >= tg->td->filtered_latency) {
         int bucket;
         unsigned int threshold;
 
         bucket = request_bucket_index(bio_issue_size(&bio->bi_issue));
         threshold = tg->td->avg_buckets[rw][bucket].latency +
             tg->latency_target;
         if (lat > threshold)
             tg->bad_bio_cnt++;
         /*
          * Not race free, could get wrong count, which means cgroups
          * will be throttled
          */
         tg->bio_cnt++;
     }
 
     if (time_after(jiffies, tg->bio_cnt_reset_time) || tg->bio_cnt > 1024) {
         tg->bio_cnt_reset_time = tg->td->throtl_slice + jiffies;
         tg->bio_cnt /= 2;
         tg->bad_bio_cnt /= 2;
     }
 }
 #endif
 
 int blk_throtl_init(struct request_queue *q)
 {
     struct throtl_data *td;
     int ret;
 
     td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
     if (!td)
         return -ENOMEM;
     td->latency_buckets[READ] = __alloc_percpu(sizeof(struct latency_bucket) *
         LATENCY_BUCKET_SIZE, __alignof__(u64));
     if (!td->latency_buckets[READ]) {
         kfree(td);
         return -ENOMEM;
     }
     td->latency_buckets[WRITE] = __alloc_percpu(sizeof(struct latency_bucket) *
         LATENCY_BUCKET_SIZE, __alignof__(u64));
     if (!td->latency_buckets[WRITE]) {
         free_percpu(td->latency_buckets[READ]);
         kfree(td);
         return -ENOMEM;
     }
 
     INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
     throtl_service_queue_init(&td->service_queue);
 
     q->td = td;
     td->queue = q;
 
     td->limit_valid[LIMIT_MAX] = true;
     td->limit_index = LIMIT_MAX;
     td->low_upgrade_time = jiffies;
     td->low_downgrade_time = jiffies;
 
     /* activate policy */
     ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
     if (ret) {
         free_percpu(td->latency_buckets[READ]);
         free_percpu(td->latency_buckets[WRITE]);
         kfree(td);
     }
     return ret;
 }
 
 void blk_throtl_exit(struct request_queue *q)
 {
     BUG_ON(!q->td);
     del_timer_sync(&q->td->service_queue.pending_timer);
     throtl_shutdown_wq(q);
     blkcg_deactivate_policy(q, &blkcg_policy_throtl);
     free_percpu(q->td->latency_buckets[READ]);
     free_percpu(q->td->latency_buckets[WRITE]);
     kfree(q->td);
 }
 
 void blk_throtl_register_queue(struct request_queue *q)
 {
     struct throtl_data *td;
     int i;
 
     td = q->td;
     BUG_ON(!td);
 
     if (blk_queue_nonrot(q)) {
         td->throtl_slice = DFL_THROTL_SLICE_SSD;
         td->filtered_latency = LATENCY_FILTERED_SSD;
     } else {
         td->throtl_slice = DFL_THROTL_SLICE_HD;
         td->filtered_latency = LATENCY_FILTERED_HD;
         for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
             td->avg_buckets[READ][i].latency = DFL_HD_BASELINE_LATENCY;
             td->avg_buckets[WRITE][i].latency = DFL_HD_BASELINE_LATENCY;
         }
     }
 #ifndef CONFIG_BLK_DEV_THROTTLING_LOW
     /* if no low limit, use previous default */
     td->throtl_slice = DFL_THROTL_SLICE_HD;
 #endif
 
     td->track_bio_latency = !queue_is_mq(q);
     if (!td->track_bio_latency)
         blk_stat_enable_accounting(q);
 }
 
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 ssize_t blk_throtl_sample_time_show(struct request_queue *q, char *page)
 {
     if (!q->td)
         return -EINVAL;
     return sprintf(page, "%u\n", jiffies_to_msecs(q->td->throtl_slice));
 }
 
 ssize_t blk_throtl_sample_time_store(struct request_queue *q,
     const char *page, size_t count)
 {
     unsigned long v;
     unsigned long t;
 
     if (!q->td)
         return -EINVAL;
     if (kstrtoul(page, 10, &v))
         return -EINVAL;
     t = msecs_to_jiffies(v);
     if (t == 0 || t > MAX_THROTL_SLICE)
         return -EINVAL;
     q->td->throtl_slice = t;
     return count;
 }
 #endif
 
 static int __init throtl_init(void)
 {
     kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
     if (!kthrotld_workqueue)
         panic("Failed to create kthrotld\n");
 
     return blkcg_policy_register(&blkcg_policy_throtl);
 }
 
 module_init(throtl_init);