linux/drivers/md/dm-queue-length.c
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   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
  29struct selector {
  30        struct list_head        valid_paths;
  31        struct list_head        failed_paths;
  32        spinlock_t lock;
  33};
  34
  35struct 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
  42static 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
  55static 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
  66static 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
  76static 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
  86static 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
 111static 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
 160static 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
 171static 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 */
 187static 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        /* Change preferred (first in list) path to evenly balance. */
 199        list_move_tail(s->valid_paths.next, &s->valid_paths);
 200
 201        list_for_each_entry(pi, &s->valid_paths, list) {
 202                if (!best ||
 203                    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
 204                        best = pi;
 205
 206                if (!atomic_read(&best->qlen))
 207                        break;
 208        }
 209
 210        if (!best)
 211                goto out;
 212
 213        ret = best->path;
 214out:
 215        spin_unlock_irqrestore(&s->lock, flags);
 216        return ret;
 217}
 218
 219static 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
 229static 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
 239static 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
 255static 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
 267static 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
 275module_init(dm_ql_init);
 276module_exit(dm_ql_exit);
 277
 278MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
 279MODULE_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);
 283MODULE_LICENSE("GPL");
 284