drivers/md/dm-queue-length.c

   1 /*
   2  * Copyright (C) 2004-2005 IBM Corp.  All Rights Reserved.
   3  * Copyright (C) 2006-2009 NEC Corporation.
   4  *
   5  * dm-queue-length.c
   6  *
   7  * Module Author: Stefan Bader, IBM
   8  * Modified by: Kiyoshi Ueda, NEC
   9  *
  10  * This file is released under the GPL.
  11  *
  12  * queue-length path selector - choose a path with the least number of
  13  * in-flight I/Os.
  14  */
  15
  16 #include "dm.h"
  17 #include "dm-path-selector.h"
  18
  19 #include <linux/slab.h>
  20 #include <linux/ctype.h>
  21 #include <linux/errno.h>
  22 #include <linux/module.h>
  23 #include <linux/atomic.h>
  24
  25 #define DM_MSG_PREFIX   "multipath queue-length"
  26 #define QL_MIN_IO       1
  27 #define QL_VERSION      "0.2.0"
  28
  29 struct selector {
  30         struct list_head        valid_paths;
  31         struct list_head        failed_paths;
  32         spinlock_t lock;
  33 };
  34
  35 struct path_info {
  36         struct list_head        list;
  37         struct dm_path          *path;
  38         unsigned                repeat_count;
  39         atomic_t                qlen;   /* the number of in-flight I/Os */
  40 };
  41
  42 static struct selector *alloc_selector(void)
  43 {
  44         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  45
  46         if (s) {
  47                 INIT_LIST_HEAD(&s->valid_paths);
  48                 INIT_LIST_HEAD(&s->failed_paths);
  49                 spin_lock_init(&s->lock);
  50         }
  51
  52         return s;
  53 }
  54
  55 static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
  56 {
  57         struct selector *s = alloc_selector();
  58
  59         if (!s)
  60                 return -ENOMEM;
  61
  62         ps->context = s;
  63         return 0;
  64 }
  65
  66 static void ql_free_paths(struct list_head *paths)
  67 {
  68         struct path_info *pi, *next;
  69
  70         list_for_each_entry_safe(pi, next, paths, list) {
  71                 list_del(&pi->list);
  72                 kfree(pi);
  73         }
  74 }
  75
  76 static void ql_destroy(struct path_selector *ps)
  77 {
  78         struct selector *s = ps->context;
  79
  80         ql_free_paths(&s->valid_paths);
  81         ql_free_paths(&s->failed_paths);
  82         kfree(s);
  83         ps->context = NULL;
  84 }
  85
  86 static int ql_status(struct path_selector *ps, struct dm_path *path,
  87                      status_type_t type, char *result, unsigned maxlen)
  88 {
  89         unsigned sz = 0;
  90         struct path_info *pi;
  91
  92         /* When called with NULL path, return selector status/args. */
  93         if (!path)
  94                 DMEMIT("0 ");
  95         else {
  96                 pi = path->pscontext;
  97
  98                 switch (type) {
  99                 case STATUSTYPE_INFO:
 100                         DMEMIT("%d ", atomic_read(&pi->qlen));
 101                         break;
 102                 case STATUSTYPE_TABLE:
 103                         DMEMIT("%u ", pi->repeat_count);
 104                         break;
 105                 }
 106         }
 107
 108         return sz;
 109 }
 110
 111 static int ql_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 = QL_MIN_IO;
 117         char dummy;
 118         unsigned long flags;
 119
 120         /*
 121          * Arguments: [<repeat_count>]
 122          *      <repeat_count>: The number of I/Os before switching path.
 123          *                      If not given, default (QL_MIN_IO) is used.
 124          */
 125         if (argc > 1) {
 126                 *error = "queue-length ps: incorrect number of arguments";
 127                 return -EINVAL;
 128         }
 129
 130         if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 131                 *error = "queue-length ps: invalid repeat count";
 132                 return -EINVAL;
 133         }
 134
 135         if (repeat_count > 1) {
 136                 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
 137                 repeat_count = 1;
 138         }
 139
 140         /* Allocate the path information structure */
 141         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 142         if (!pi) {
 143                 *error = "queue-length ps: Error allocating path information";
 144                 return -ENOMEM;
 145         }
 146
 147         pi->path = path;
 148         pi->repeat_count = repeat_count;
 149         atomic_set(&pi->qlen, 0);
 150
 151         path->pscontext = pi;
 152
 153         spin_lock_irqsave(&s->lock, flags);
 154         list_add_tail(&pi->list, &s->valid_paths);
 155         spin_unlock_irqrestore(&s->lock, flags);
 156
 157         return 0;
 158 }
 159
 160 static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
 161 {
 162         struct selector *s = ps->context;
 163         struct path_info *pi = path->pscontext;
 164         unsigned long flags;
 165
 166         spin_lock_irqsave(&s->lock, flags);
 167         list_move(&pi->list, &s->failed_paths);
 168         spin_unlock_irqrestore(&s->lock, flags);
 169 }
 170
 171 static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
 172 {
 173         struct selector *s = ps->context;
 174         struct path_info *pi = path->pscontext;
 175         unsigned long flags;
 176
 177         spin_lock_irqsave(&s->lock, flags);
 178         list_move_tail(&pi->list, &s->valid_paths);
 179         spin_unlock_irqrestore(&s->lock, flags);
 180
 181         return 0;
 182 }
 183
 184 /*
 185  * Select a path having the minimum number of in-flight I/Os
 186  */
 187 static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes)
 188 {
 189         struct selector *s = ps->context;
 190         struct path_info *pi = NULL, *best = NULL;
 191         struct dm_path *ret = NULL;
 192         unsigned long flags;
 193
 194         spin_lock_irqsave(&s->lock, flags);
 195         if (list_empty(&s->valid_paths))
 196                 goto out;
 197
 198         list_for_each_entry(pi, &s->valid_paths, list) {
 199                 if (!best ||
 200                     (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
 201                         best = pi;
 202
 203                 if (!atomic_read(&best->qlen))
 204                         break;
 205         }
 206
 207         if (!best)
 208                 goto out;
 209
 210         /* Move most recently used to least preferred to evenly balance. */
 211         list_move_tail(&best->list, &s->valid_paths);
 212
 213         ret = best->path;
 214 out:
 215         spin_unlock_irqrestore(&s->lock, flags);
 216         return ret;
 217 }
 218
 219 static int ql_start_io(struct path_selector *ps, struct dm_path *path,
 220                        size_t nr_bytes)
 221 {
 222         struct path_info *pi = path->pscontext;
 223
 224         atomic_inc(&pi->qlen);
 225
 226         return 0;
 227 }
 228
 229 static int ql_end_io(struct path_selector *ps, struct dm_path *path,
 230                      size_t nr_bytes)
 231 {
 232         struct path_info *pi = path->pscontext;
 233
 234         atomic_dec(&pi->qlen);
 235
 236         return 0;
 237 }
 238
 239 static struct path_selector_type ql_ps = {
 240         .name           = "queue-length",
 241         .module         = THIS_MODULE,
 242         .table_args     = 1,
 243         .info_args      = 1,
 244         .create         = ql_create,
 245         .destroy        = ql_destroy,
 246         .status         = ql_status,
 247         .add_path       = ql_add_path,
 248         .fail_path      = ql_fail_path,
 249         .reinstate_path = ql_reinstate_path,
 250         .select_path    = ql_select_path,
 251         .start_io       = ql_start_io,
 252         .end_io         = ql_end_io,
 253 };
 254
 255 static int __init dm_ql_init(void)
 256 {
 257         int r = dm_register_path_selector(&ql_ps);
 258
 259         if (r < 0)
 260                 DMERR("register failed %d", r);
 261
 262         DMINFO("version " QL_VERSION " loaded");
 263
 264         return r;
 265 }
 266
 267 static void __exit dm_ql_exit(void)
 268 {
 269         int r = dm_unregister_path_selector(&ql_ps);
 270
 271         if (r < 0)
 272                 DMERR("unregister failed %d", r);
 273 }
 274
 275 module_init(dm_ql_init);
 276 module_exit(dm_ql_exit);
 277
 278 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
 279 MODULE_DESCRIPTION(
 280         "(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
 281         DM_NAME " path selector to balance the number of in-flight I/Os"
 282 );
 283 MODULE_LICENSE("GPL");