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       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         char dummy;
 116
 117         /*
 118          * Arguments: [<repeat_count>]
 119          *      <repeat_count>: The number of I/Os before switching path.
 120          *                      If not given, default (QL_MIN_IO) is used.
 121          */
 122         if (argc > 1) {
 123                 *error = "queue-length ps: incorrect number of arguments";
 124                 return -EINVAL;
 125         }
 126
 127         if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 128                 *error = "queue-length ps: invalid repeat count";
 129                 return -EINVAL;
 130         }
 131
 132         /* Allocate the path information structure */
 133         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 134         if (!pi) {
 135                 *error = "queue-length ps: Error allocating path information";
 136                 return -ENOMEM;
 137         }
 138
 139         pi->path = path;
 140         pi->repeat_count = repeat_count;
 141         atomic_set(&pi->qlen, 0);
 142
 143         path->pscontext = pi;
 144
 145         list_add_tail(&pi->list, &s->valid_paths);
 146
 147         return 0;
 148 }
 149
 150 static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
 151 {
 152         struct selector *s = ps->context;
 153         struct path_info *pi = path->pscontext;
 154
 155         list_move(&pi->list, &s->failed_paths);
 156 }
 157
 158 static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
 159 {
 160         struct selector *s = ps->context;
 161         struct path_info *pi = path->pscontext;
 162
 163         list_move_tail(&pi->list, &s->valid_paths);
 164
 165         return 0;
 166 }
 167
 168 /*
 169  * Select a path having the minimum number of in-flight I/Os
 170  */
 171 static struct dm_path *ql_select_path(struct path_selector *ps,
 172                                       unsigned *repeat_count, size_t nr_bytes)
 173 {
 174         struct selector *s = ps->context;
 175         struct path_info *pi = NULL, *best = NULL;
 176
 177         if (list_empty(&s->valid_paths))
 178                 return NULL;
 179
 180         /* Change preferred (first in list) path to evenly balance. */
 181         list_move_tail(s->valid_paths.next, &s->valid_paths);
 182
 183         list_for_each_entry(pi, &s->valid_paths, list) {
 184                 if (!best ||
 185                     (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
 186                         best = pi;
 187
 188                 if (!atomic_read(&best->qlen))
 189                         break;
 190         }
 191
 192         if (!best)
 193                 return NULL;
 194
 195         *repeat_count = best->repeat_count;
 196
 197         return best->path;
 198 }
 199
 200 static int ql_start_io(struct path_selector *ps, struct dm_path *path,
 201                        size_t nr_bytes)
 202 {
 203         struct path_info *pi = path->pscontext;
 204
 205         atomic_inc(&pi->qlen);
 206
 207         return 0;
 208 }
 209
 210 static int ql_end_io(struct path_selector *ps, struct dm_path *path,
 211                      size_t nr_bytes)
 212 {
 213         struct path_info *pi = path->pscontext;
 214
 215         atomic_dec(&pi->qlen);
 216
 217         return 0;
 218 }
 219
 220 static struct path_selector_type ql_ps = {
 221         .name           = "queue-length",
 222         .module         = THIS_MODULE,
 223         .table_args     = 1,
 224         .info_args      = 1,
 225         .create         = ql_create,
 226         .destroy        = ql_destroy,
 227         .status         = ql_status,
 228         .add_path       = ql_add_path,
 229         .fail_path      = ql_fail_path,
 230         .reinstate_path = ql_reinstate_path,
 231         .select_path    = ql_select_path,
 232         .start_io       = ql_start_io,
 233         .end_io         = ql_end_io,
 234 };
 235
 236 static int __init dm_ql_init(void)
 237 {
 238         int r = dm_register_path_selector(&ql_ps);
 239
 240         if (r < 0)
 241                 DMERR("register failed %d", r);
 242
 243         DMINFO("version " QL_VERSION " loaded");
 244
 245         return r;
 246 }
 247
 248 static void __exit dm_ql_exit(void)
 249 {
 250         int r = dm_unregister_path_selector(&ql_ps);
 251
 252         if (r < 0)
 253                 DMERR("unregister failed %d", r);
 254 }
 255
 256 module_init(dm_ql_init);
 257 module_exit(dm_ql_exit);
 258
 259 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
 260 MODULE_DESCRIPTION(
 261         "(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
 262         DM_NAME " path selector to balance the number of in-flight I/Os"
 263 );
 264 MODULE_LICENSE("GPL");