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 <asm/atomic.h>
  24
  25 #define DM_MSG_PREFIX   "multipath queue-length"
  26 #define QL_MIN_IO       128
  27 #define QL_VERSION      "0.1.0"
  28
  29 struct selector {
  30         struct list_head        valid_paths;
  31         struct list_head        failed_paths;
  32 };
  33
  34 struct path_info {
  35         struct list_head        list;
  36         struct dm_path          *path;
  37         unsigned                repeat_count;
  38         atomic_t                qlen;   /* the number of in-flight I/Os */
  39 };
  40
  41 static struct selector *alloc_selector(void)
  42 {
  43         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  44
  45         if (s) {
  46                 INIT_LIST_HEAD(&s->valid_paths);
  47                 INIT_LIST_HEAD(&s->failed_paths);
  48         }
  49
  50         return s;
  51 }
  52
  53 static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
  54 {
  55         struct selector *s = alloc_selector();
  56
  57         if (!s)
  58                 return -ENOMEM;
  59
  60         ps->context = s;
  61         return 0;
  62 }
  63
  64 static void ql_free_paths(struct list_head *paths)
  65 {
  66         struct path_info *pi, *next;
  67
  68         list_for_each_entry_safe(pi, next, paths, list) {
  69                 list_del(&pi->list);
  70                 kfree(pi);
  71         }
  72 }
  73
  74 static void ql_destroy(struct path_selector *ps)
  75 {
  76         struct selector *s = ps->context;
  77
  78         ql_free_paths(&s->valid_paths);
  79         ql_free_paths(&s->failed_paths);
  80         kfree(s);
  81         ps->context = NULL;
  82 }
  83
  84 static int ql_status(struct path_selector *ps, struct dm_path *path,
  85                      status_type_t type, char *result, unsigned maxlen)
  86 {
  87         unsigned sz = 0;
  88         struct path_info *pi;
  89
  90         /* When called with NULL path, return selector status/args. */
  91         if (!path)
  92                 DMEMIT("0 ");
  93         else {
  94                 pi = path->pscontext;
  95
  96                 switch (type) {
  97                 case STATUSTYPE_INFO:
  98                         DMEMIT("%d ", atomic_read(&pi->qlen));
  99                         break;
 100                 case STATUSTYPE_TABLE:
 101                         DMEMIT("%u ", pi->repeat_count);
 102                         break;
 103                 }
 104         }
 105
 106         return sz;
 107 }
 108
 109 static int ql_add_path(struct path_selector *ps, struct dm_path *path,
 110                        int argc, char **argv, char **error)
 111 {
 112         struct selector *s = ps->context;
 113         struct path_info *pi;
 114         unsigned repeat_count = QL_MIN_IO;
 115
 116         /*
 117          * Arguments: [<repeat_count>]
 118          *      <repeat_count>: The number of I/Os before switching path.
 119          *                      If not given, default (QL_MIN_IO) is used.
 120          */
 121         if (argc > 1) {
 122                 *error = "queue-length ps: incorrect number of arguments";
 123                 return -EINVAL;
 124         }
 125
 126         if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
 127                 *error = "queue-length ps: invalid repeat count";
 128                 return -EINVAL;
 129         }
 130
 131         /* Allocate the path information structure */
 132         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 133         if (!pi) {
 134                 *error = "queue-length ps: Error allocating path information";
 135                 return -ENOMEM;
 136         }
 137
 138         pi->path = path;
 139         pi->repeat_count = repeat_count;
 140         atomic_set(&pi->qlen, 0);
 141
 142         path->pscontext = pi;
 143
 144         list_add_tail(&pi->list, &s->valid_paths);
 145
 146         return 0;
 147 }
 148
 149 static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
 150 {
 151         struct selector *s = ps->context;
 152         struct path_info *pi = path->pscontext;
 153
 154         list_move(&pi->list, &s->failed_paths);
 155 }
 156
 157 static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
 158 {
 159         struct selector *s = ps->context;
 160         struct path_info *pi = path->pscontext;
 161
 162         list_move_tail(&pi->list, &s->valid_paths);
 163
 164         return 0;
 165 }
 166
 167 /*
 168  * Select a path having the minimum number of in-flight I/Os
 169  */
 170 static struct dm_path *ql_select_path(struct path_selector *ps,
 171                                       unsigned *repeat_count, size_t nr_bytes)
 172 {
 173         struct selector *s = ps->context;
 174         struct path_info *pi = NULL, *best = NULL;
 175
 176         if (list_empty(&s->valid_paths))
 177                 return NULL;
 178
 179         /* Change preferred (first in list) path to evenly balance. */
 180         list_move_tail(s->valid_paths.next, &s->valid_paths);
 181
 182         list_for_each_entry(pi, &s->valid_paths, list) {
 183                 if (!best ||
 184                     (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
 185                         best = pi;
 186
 187                 if (!atomic_read(&best->qlen))
 188                         break;
 189         }
 190
 191         if (!best)
 192                 return NULL;
 193
 194         *repeat_count = best->repeat_count;
 195
 196         return best->path;
 197 }
 198
 199 static int ql_start_io(struct path_selector *ps, struct dm_path *path,
 200                        size_t nr_bytes)
 201 {
 202         struct path_info *pi = path->pscontext;
 203
 204         atomic_inc(&pi->qlen);
 205
 206         return 0;
 207 }
 208
 209 static int ql_end_io(struct path_selector *ps, struct dm_path *path,
 210                      size_t nr_bytes)
 211 {
 212         struct path_info *pi = path->pscontext;
 213
 214         atomic_dec(&pi->qlen);
 215
 216         return 0;
 217 }
 218
 219 static struct path_selector_type ql_ps = {
 220         .name           = "queue-length",
 221         .module         = THIS_MODULE,
 222         .table_args     = 1,
 223         .info_args      = 1,
 224         .create         = ql_create,
 225         .destroy        = ql_destroy,
 226         .status         = ql_status,
 227         .add_path       = ql_add_path,
 228         .fail_path      = ql_fail_path,
 229         .reinstate_path = ql_reinstate_path,
 230         .select_path    = ql_select_path,
 231         .start_io       = ql_start_io,
 232         .end_io         = ql_end_io,
 233 };
 234
 235 static int __init dm_ql_init(void)
 236 {
 237         int r = dm_register_path_selector(&ql_ps);
 238
 239         if (r < 0)
 240                 DMERR("register failed %d", r);
 241
 242         DMINFO("version " QL_VERSION " loaded");
 243
 244         return r;
 245 }
 246
 247 static void __exit dm_ql_exit(void)
 248 {
 249         int r = dm_unregister_path_selector(&ql_ps);
 250
 251         if (r < 0)
 252                 DMERR("unregister failed %d", r);
 253 }
 254
 255 module_init(dm_ql_init);
 256 module_exit(dm_ql_exit);
 257
 258 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
 259 MODULE_DESCRIPTION(
 260         "(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
 261         DM_NAME " path selector to balance the number of in-flight I/Os"
 262 );
 263 MODULE_LICENSE("GPL");