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

   1 /*
   2  * Copyright (C) 2007-2009 NEC Corporation.  All Rights Reserved.
   3  *
   4  * Module Author: Kiyoshi Ueda
   5  *
   6  * This file is released under the GPL.
   7  *
   8  * Throughput oriented path selector.
   9  */
  10
  11 #include "dm.h"
  12 #include "dm-path-selector.h"
  13
  14 #include <linux/slab.h>
  15 #include <linux/module.h>
  16
  17 #define DM_MSG_PREFIX   "multipath service-time"
  18 #define ST_MIN_IO       1
  19 #define ST_MAX_RELATIVE_THROUGHPUT      100
  20 #define ST_MAX_RELATIVE_THROUGHPUT_SHIFT        7
  21 #define ST_MAX_INFLIGHT_SIZE    ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
  22 #define ST_VERSION      "0.3.0"
  23
  24 struct selector {
  25         struct list_head valid_paths;
  26         struct list_head failed_paths;
  27         spinlock_t lock;
  28 };
  29
  30 struct path_info {
  31         struct list_head list;
  32         struct dm_path *path;
  33         unsigned repeat_count;
  34         unsigned relative_throughput;
  35         atomic_t in_flight_size;        /* Total size of in-flight I/Os */
  36 };
  37
  38 static struct selector *alloc_selector(void)
  39 {
  40         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  41
  42         if (s) {
  43                 INIT_LIST_HEAD(&s->valid_paths);
  44                 INIT_LIST_HEAD(&s->failed_paths);
  45                 spin_lock_init(&s->lock);
  46         }
  47
  48         return s;
  49 }
  50
  51 static int st_create(struct path_selector *ps, unsigned argc, char **argv)
  52 {
  53         struct selector *s = alloc_selector();
  54
  55         if (!s)
  56                 return -ENOMEM;
  57
  58         ps->context = s;
  59         return 0;
  60 }
  61
  62 static void free_paths(struct list_head *paths)
  63 {
  64         struct path_info *pi, *next;
  65
  66         list_for_each_entry_safe(pi, next, paths, list) {
  67                 list_del(&pi->list);
  68                 kfree(pi);
  69         }
  70 }
  71
  72 static void st_destroy(struct path_selector *ps)
  73 {
  74         struct selector *s = ps->context;
  75
  76         free_paths(&s->valid_paths);
  77         free_paths(&s->failed_paths);
  78         kfree(s);
  79         ps->context = NULL;
  80 }
  81
  82 static int st_status(struct path_selector *ps, struct dm_path *path,
  83                      status_type_t type, char *result, unsigned maxlen)
  84 {
  85         unsigned sz = 0;
  86         struct path_info *pi;
  87
  88         if (!path)
  89                 DMEMIT("0 ");
  90         else {
  91                 pi = path->pscontext;
  92
  93                 switch (type) {
  94                 case STATUSTYPE_INFO:
  95                         DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
  96                                pi->relative_throughput);
  97                         break;
  98                 case STATUSTYPE_TABLE:
  99                         DMEMIT("%u %u ", pi->repeat_count,
 100                                pi->relative_throughput);
 101                         break;
 102                 case STATUSTYPE_IMA:
 103                         result[0] = '\0';
 104                         break;
 105                 }
 106         }
 107
 108         return sz;
 109 }
 110
 111 static int st_add_path(struct path_selector *ps, struct dm_path *path,
 112                        int argc, char **argv, char **error)
 113 {
 114         struct selector *s = ps->context;
 115         struct path_info *pi;
 116         unsigned repeat_count = ST_MIN_IO;
 117         unsigned relative_throughput = 1;
 118         char dummy;
 119         unsigned long flags;
 120
 121         /*
 122          * Arguments: [<repeat_count> [<relative_throughput>]]
 123          *      <repeat_count>: The number of I/Os before switching path.
 124          *                      If not given, default (ST_MIN_IO) is used.
 125          *      <relative_throughput>: The relative throughput value of
 126          *                      the path among all paths in the path-group.
 127          *                      The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
 128          *                      If not given, minimum value '1' is used.
 129          *                      If '0' is given, the path isn't selected while
 130          *                      other paths having a positive value are
 131          *                      available.
 132          */
 133         if (argc > 2) {
 134                 *error = "service-time ps: incorrect number of arguments";
 135                 return -EINVAL;
 136         }
 137
 138         if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 139                 *error = "service-time ps: invalid repeat count";
 140                 return -EINVAL;
 141         }
 142
 143         if (repeat_count > 1) {
 144                 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
 145                 repeat_count = 1;
 146         }
 147
 148         if ((argc == 2) &&
 149             (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
 150              relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
 151                 *error = "service-time ps: invalid relative_throughput value";
 152                 return -EINVAL;
 153         }
 154
 155         /* allocate the path */
 156         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 157         if (!pi) {
 158                 *error = "service-time ps: Error allocating path context";
 159                 return -ENOMEM;
 160         }
 161
 162         pi->path = path;
 163         pi->repeat_count = repeat_count;
 164         pi->relative_throughput = relative_throughput;
 165         atomic_set(&pi->in_flight_size, 0);
 166
 167         path->pscontext = pi;
 168
 169         spin_lock_irqsave(&s->lock, flags);
 170         list_add_tail(&pi->list, &s->valid_paths);
 171         spin_unlock_irqrestore(&s->lock, flags);
 172
 173         return 0;
 174 }
 175
 176 static void st_fail_path(struct path_selector *ps, struct dm_path *path)
 177 {
 178         struct selector *s = ps->context;
 179         struct path_info *pi = path->pscontext;
 180         unsigned long flags;
 181
 182         spin_lock_irqsave(&s->lock, flags);
 183         list_move(&pi->list, &s->failed_paths);
 184         spin_unlock_irqrestore(&s->lock, flags);
 185 }
 186
 187 static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
 188 {
 189         struct selector *s = ps->context;
 190         struct path_info *pi = path->pscontext;
 191         unsigned long flags;
 192
 193         spin_lock_irqsave(&s->lock, flags);
 194         list_move_tail(&pi->list, &s->valid_paths);
 195         spin_unlock_irqrestore(&s->lock, flags);
 196
 197         return 0;
 198 }
 199
 200 /*
 201  * Compare the estimated service time of 2 paths, pi1 and pi2,
 202  * for the incoming I/O.
 203  *
 204  * Returns:
 205  * < 0 : pi1 is better
 206  * 0   : no difference between pi1 and pi2
 207  * > 0 : pi2 is better
 208  *
 209  * Description:
 210  * Basically, the service time is estimated by:
 211  *     ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
 212  * To reduce the calculation, some optimizations are made.
 213  * (See comments inline)
 214  */
 215 static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
 216                            size_t incoming)
 217 {
 218         size_t sz1, sz2, st1, st2;
 219
 220         sz1 = atomic_read(&pi1->in_flight_size);
 221         sz2 = atomic_read(&pi2->in_flight_size);
 222
 223         /*
 224          * Case 1: Both have same throughput value. Choose less loaded path.
 225          */
 226         if (pi1->relative_throughput == pi2->relative_throughput)
 227                 return sz1 - sz2;
 228
 229         /*
 230          * Case 2a: Both have same load. Choose higher throughput path.
 231          * Case 2b: One path has no throughput value. Choose the other one.
 232          */
 233         if (sz1 == sz2 ||
 234             !pi1->relative_throughput || !pi2->relative_throughput)
 235                 return pi2->relative_throughput - pi1->relative_throughput;
 236
 237         /*
 238          * Case 3: Calculate service time. Choose faster path.
 239          *         Service time using pi1:
 240          *             st1 = (sz1 + incoming) / pi1->relative_throughput
 241          *         Service time using pi2:
 242          *             st2 = (sz2 + incoming) / pi2->relative_throughput
 243          *
 244          *         To avoid the division, transform the expression to use
 245          *         multiplication.
 246          *         Because ->relative_throughput > 0 here, if st1 < st2,
 247          *         the expressions below are the same meaning:
 248          *             (sz1 + incoming) / pi1->relative_throughput <
 249          *                 (sz2 + incoming) / pi2->relative_throughput
 250          *             (sz1 + incoming) * pi2->relative_throughput <
 251          *                 (sz2 + incoming) * pi1->relative_throughput
 252          *         So use the later one.
 253          */
 254         sz1 += incoming;
 255         sz2 += incoming;
 256         if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
 257                      sz2 >= ST_MAX_INFLIGHT_SIZE)) {
 258                 /*
 259                  * Size may be too big for multiplying pi->relative_throughput
 260                  * and overflow.
 261                  * To avoid the overflow and mis-selection, shift down both.
 262                  */
 263                 sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
 264                 sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
 265         }
 266         st1 = sz1 * pi2->relative_throughput;
 267         st2 = sz2 * pi1->relative_throughput;
 268         if (st1 != st2)
 269                 return st1 - st2;
 270
 271         /*
 272          * Case 4: Service time is equal. Choose higher throughput path.
 273          */
 274         return pi2->relative_throughput - pi1->relative_throughput;
 275 }
 276
 277 static struct dm_path *st_select_path(struct path_selector *ps, size_t nr_bytes)
 278 {
 279         struct selector *s = ps->context;
 280         struct path_info *pi = NULL, *best = NULL;
 281         struct dm_path *ret = NULL;
 282         unsigned long flags;
 283
 284         spin_lock_irqsave(&s->lock, flags);
 285         if (list_empty(&s->valid_paths))
 286                 goto out;
 287
 288         list_for_each_entry(pi, &s->valid_paths, list)
 289                 if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
 290                         best = pi;
 291
 292         if (!best)
 293                 goto out;
 294
 295         /* Move most recently used to least preferred to evenly balance. */
 296         list_move_tail(&best->list, &s->valid_paths);
 297
 298         ret = best->path;
 299 out:
 300         spin_unlock_irqrestore(&s->lock, flags);
 301         return ret;
 302 }
 303
 304 static int st_start_io(struct path_selector *ps, struct dm_path *path,
 305                        size_t nr_bytes)
 306 {
 307         struct path_info *pi = path->pscontext;
 308
 309         atomic_add(nr_bytes, &pi->in_flight_size);
 310
 311         return 0;
 312 }
 313
 314 static int st_end_io(struct path_selector *ps, struct dm_path *path,
 315                      size_t nr_bytes, u64 start_time)
 316 {
 317         struct path_info *pi = path->pscontext;
 318
 319         atomic_sub(nr_bytes, &pi->in_flight_size);
 320
 321         return 0;
 322 }
 323
 324 static struct path_selector_type st_ps = {
 325         .name           = "service-time",
 326         .module         = THIS_MODULE,
 327         .table_args     = 2,
 328         .info_args      = 2,
 329         .create         = st_create,
 330         .destroy        = st_destroy,
 331         .status         = st_status,
 332         .add_path       = st_add_path,
 333         .fail_path      = st_fail_path,
 334         .reinstate_path = st_reinstate_path,
 335         .select_path    = st_select_path,
 336         .start_io       = st_start_io,
 337         .end_io         = st_end_io,
 338 };
 339
 340 static int __init dm_st_init(void)
 341 {
 342         int r = dm_register_path_selector(&st_ps);
 343
 344         if (r < 0)
 345                 DMERR("register failed %d", r);
 346
 347         DMINFO("version " ST_VERSION " loaded");
 348
 349         return r;
 350 }
 351
 352 static void __exit dm_st_exit(void)
 353 {
 354         int r = dm_unregister_path_selector(&st_ps);
 355
 356         if (r < 0)
 357                 DMERR("unregister failed %d", r);
 358 }
 359
 360 module_init(dm_st_init);
 361 module_exit(dm_st_exit);
 362
 363 MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
 364 MODULE_AUTHOR("Kiyoshi Ueda <[email protected]>");
 365 MODULE_LICENSE("GPL");