drivers/md/dm-ps-service-time.c

0001 /*
0002  * Copyright (C) 2007-2009 NEC Corporation.  All Rights Reserved.
0003  *
0004  * Module Author: Kiyoshi Ueda
0005  *
0006  * This file is released under the GPL.
0007  *
0008  * Throughput oriented path selector.
0009  */
0010
0011 #include "dm.h"
0012 #include "dm-path-selector.h"
0013
0014 #include <linux/slab.h>
0015 #include <linux/module.h>
0016
0017 #define DM_MSG_PREFIX   "multipath service-time"
0018 #define ST_MIN_IO   1
0019 #define ST_MAX_RELATIVE_THROUGHPUT  100
0020 #define ST_MAX_RELATIVE_THROUGHPUT_SHIFT    7
0021 #define ST_MAX_INFLIGHT_SIZE    ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
0022 #define ST_VERSION  "0.3.0"
0023
0024 struct selector {
0025     struct list_head valid_paths;
0026     struct list_head failed_paths;
0027     spinlock_t lock;
0028 };
0029
0030 struct path_info {
0031     struct list_head list;
0032     struct dm_path *path;
0033     unsigned repeat_count;
0034     unsigned relative_throughput;
0035     atomic_t in_flight_size;    /* Total size of in-flight I/Os */
0036 };
0037
0038 static struct selector *alloc_selector(void)
0039 {
0040     struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
0041
0042     if (s) {
0043         INIT_LIST_HEAD(&s->valid_paths);
0044         INIT_LIST_HEAD(&s->failed_paths);
0045         spin_lock_init(&s->lock);
0046     }
0047
0048     return s;
0049 }
0050
0051 static int st_create(struct path_selector *ps, unsigned argc, char **argv)
0052 {
0053     struct selector *s = alloc_selector();
0054
0055     if (!s)
0056         return -ENOMEM;
0057
0058     ps->context = s;
0059     return 0;
0060 }
0061
0062 static void free_paths(struct list_head *paths)
0063 {
0064     struct path_info *pi, *next;
0065
0066     list_for_each_entry_safe(pi, next, paths, list) {
0067         list_del(&pi->list);
0068         kfree(pi);
0069     }
0070 }
0071
0072 static void st_destroy(struct path_selector *ps)
0073 {
0074     struct selector *s = ps->context;
0075
0076     free_paths(&s->valid_paths);
0077     free_paths(&s->failed_paths);
0078     kfree(s);
0079     ps->context = NULL;
0080 }
0081
0082 static int st_status(struct path_selector *ps, struct dm_path *path,
0083              status_type_t type, char *result, unsigned maxlen)
0084 {
0085     unsigned sz = 0;
0086     struct path_info *pi;
0087
0088     if (!path)
0089         DMEMIT("0 ");
0090     else {
0091         pi = path->pscontext;
0092
0093         switch (type) {
0094         case STATUSTYPE_INFO:
0095             DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
0096                    pi->relative_throughput);
0097             break;
0098         case STATUSTYPE_TABLE:
0099             DMEMIT("%u %u ", pi->repeat_count,
0100                    pi->relative_throughput);
0101             break;
0102         case STATUSTYPE_IMA:
0103             result[0] = '\0';
0104             break;
0105         }
0106     }
0107
0108     return sz;
0109 }
0110
0111 static int st_add_path(struct path_selector *ps, struct dm_path *path,
0112                int argc, char **argv, char **error)
0113 {
0114     struct selector *s = ps->context;
0115     struct path_info *pi;
0116     unsigned repeat_count = ST_MIN_IO;
0117     unsigned relative_throughput = 1;
0118     char dummy;
0119     unsigned long flags;
0120
0121     /*
0122      * Arguments: [<repeat_count> [<relative_throughput>]]
0123      *  <repeat_count>: The number of I/Os before switching path.
0124      *          If not given, default (ST_MIN_IO) is used.
0125      *  <relative_throughput>: The relative throughput value of
0126      *          the path among all paths in the path-group.
0127      *          The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
0128      *          If not given, minimum value '1' is used.
0129      *          If '0' is given, the path isn't selected while
0130      *          other paths having a positive value are
0131      *          available.
0132      */
0133     if (argc > 2) {
0134         *error = "service-time ps: incorrect number of arguments";
0135         return -EINVAL;
0136     }
0137
0138     if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
0139         *error = "service-time ps: invalid repeat count";
0140         return -EINVAL;
0141     }
0142
0143     if (repeat_count > 1) {
0144         DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
0145         repeat_count = 1;
0146     }
0147
0148     if ((argc == 2) &&
0149         (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
0150          relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
0151         *error = "service-time ps: invalid relative_throughput value";
0152         return -EINVAL;
0153     }
0154
0155     /* allocate the path */
0156     pi = kmalloc(sizeof(*pi), GFP_KERNEL);
0157     if (!pi) {
0158         *error = "service-time ps: Error allocating path context";
0159         return -ENOMEM;
0160     }
0161
0162     pi->path = path;
0163     pi->repeat_count = repeat_count;
0164     pi->relative_throughput = relative_throughput;
0165     atomic_set(&pi->in_flight_size, 0);
0166
0167     path->pscontext = pi;
0168
0169     spin_lock_irqsave(&s->lock, flags);
0170     list_add_tail(&pi->list, &s->valid_paths);
0171     spin_unlock_irqrestore(&s->lock, flags);
0172
0173     return 0;
0174 }
0175
0176 static void st_fail_path(struct path_selector *ps, struct dm_path *path)
0177 {
0178     struct selector *s = ps->context;
0179     struct path_info *pi = path->pscontext;
0180     unsigned long flags;
0181
0182     spin_lock_irqsave(&s->lock, flags);
0183     list_move(&pi->list, &s->failed_paths);
0184     spin_unlock_irqrestore(&s->lock, flags);
0185 }
0186
0187 static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
0188 {
0189     struct selector *s = ps->context;
0190     struct path_info *pi = path->pscontext;
0191     unsigned long flags;
0192
0193     spin_lock_irqsave(&s->lock, flags);
0194     list_move_tail(&pi->list, &s->valid_paths);
0195     spin_unlock_irqrestore(&s->lock, flags);
0196
0197     return 0;
0198 }
0199
0200 /*
0201  * Compare the estimated service time of 2 paths, pi1 and pi2,
0202  * for the incoming I/O.
0203  *
0204  * Returns:
0205  * < 0 : pi1 is better
0206  * 0   : no difference between pi1 and pi2
0207  * > 0 : pi2 is better
0208  *
0209  * Description:
0210  * Basically, the service time is estimated by:
0211  *     ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
0212  * To reduce the calculation, some optimizations are made.
0213  * (See comments inline)
0214  */
0215 static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
0216                size_t incoming)
0217 {
0218     size_t sz1, sz2, st1, st2;
0219
0220     sz1 = atomic_read(&pi1->in_flight_size);
0221     sz2 = atomic_read(&pi2->in_flight_size);
0222
0223     /*
0224      * Case 1: Both have same throughput value. Choose less loaded path.
0225      */
0226     if (pi1->relative_throughput == pi2->relative_throughput)
0227         return sz1 - sz2;
0228
0229     /*
0230      * Case 2a: Both have same load. Choose higher throughput path.
0231      * Case 2b: One path has no throughput value. Choose the other one.
0232      */
0233     if (sz1 == sz2 ||
0234         !pi1->relative_throughput || !pi2->relative_throughput)
0235         return pi2->relative_throughput - pi1->relative_throughput;
0236
0237     /*
0238      * Case 3: Calculate service time. Choose faster path.
0239      *         Service time using pi1:
0240      *             st1 = (sz1 + incoming) / pi1->relative_throughput
0241      *         Service time using pi2:
0242      *             st2 = (sz2 + incoming) / pi2->relative_throughput
0243      *
0244      *         To avoid the division, transform the expression to use
0245      *         multiplication.
0246      *         Because ->relative_throughput > 0 here, if st1 < st2,
0247      *         the expressions below are the same meaning:
0248      *             (sz1 + incoming) / pi1->relative_throughput <
0249      *                 (sz2 + incoming) / pi2->relative_throughput
0250      *             (sz1 + incoming) * pi2->relative_throughput <
0251      *                 (sz2 + incoming) * pi1->relative_throughput
0252      *         So use the later one.
0253      */
0254     sz1 += incoming;
0255     sz2 += incoming;
0256     if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
0257              sz2 >= ST_MAX_INFLIGHT_SIZE)) {
0258         /*
0259          * Size may be too big for multiplying pi->relative_throughput
0260          * and overflow.
0261          * To avoid the overflow and mis-selection, shift down both.
0262          */
0263         sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
0264         sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
0265     }
0266     st1 = sz1 * pi2->relative_throughput;
0267     st2 = sz2 * pi1->relative_throughput;
0268     if (st1 != st2)
0269         return st1 - st2;
0270
0271     /*
0272      * Case 4: Service time is equal. Choose higher throughput path.
0273      */
0274     return pi2->relative_throughput - pi1->relative_throughput;
0275 }
0276
0277 static struct dm_path *st_select_path(struct path_selector *ps, size_t nr_bytes)
0278 {
0279     struct selector *s = ps->context;
0280     struct path_info *pi = NULL, *best = NULL;
0281     struct dm_path *ret = NULL;
0282     unsigned long flags;
0283
0284     spin_lock_irqsave(&s->lock, flags);
0285     if (list_empty(&s->valid_paths))
0286         goto out;
0287
0288     list_for_each_entry(pi, &s->valid_paths, list)
0289         if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
0290             best = pi;
0291
0292     if (!best)
0293         goto out;
0294
0295     /* Move most recently used to least preferred to evenly balance. */
0296     list_move_tail(&best->list, &s->valid_paths);
0297
0298     ret = best->path;
0299 out:
0300     spin_unlock_irqrestore(&s->lock, flags);
0301     return ret;
0302 }
0303
0304 static int st_start_io(struct path_selector *ps, struct dm_path *path,
0305                size_t nr_bytes)
0306 {
0307     struct path_info *pi = path->pscontext;
0308
0309     atomic_add(nr_bytes, &pi->in_flight_size);
0310
0311     return 0;
0312 }
0313
0314 static int st_end_io(struct path_selector *ps, struct dm_path *path,
0315              size_t nr_bytes, u64 start_time)
0316 {
0317     struct path_info *pi = path->pscontext;
0318
0319     atomic_sub(nr_bytes, &pi->in_flight_size);
0320
0321     return 0;
0322 }
0323
0324 static struct path_selector_type st_ps = {
0325     .name       = "service-time",
0326     .module     = THIS_MODULE,
0327     .table_args = 2,
0328     .info_args  = 2,
0329     .create     = st_create,
0330     .destroy    = st_destroy,
0331     .status     = st_status,
0332     .add_path   = st_add_path,
0333     .fail_path  = st_fail_path,
0334     .reinstate_path = st_reinstate_path,
0335     .select_path    = st_select_path,
0336     .start_io   = st_start_io,
0337     .end_io     = st_end_io,
0338 };
0339
0340 static int __init dm_st_init(void)
0341 {
0342     int r = dm_register_path_selector(&st_ps);
0343
0344     if (r < 0)
0345         DMERR("register failed %d", r);
0346
0347     DMINFO("version " ST_VERSION " loaded");
0348
0349     return r;
0350 }
0351
0352 static void __exit dm_st_exit(void)
0353 {
0354     int r = dm_unregister_path_selector(&st_ps);
0355
0356     if (r < 0)
0357         DMERR("unregister failed %d", r);
0358 }
0359
0360 module_init(dm_st_init);
0361 module_exit(dm_st_exit);
0362
0363 MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
0364 MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
0365 MODULE_LICENSE("GPL");