2 * Copyright (C) 2004-2005 IBM Corp. All Rights Reserved.
3 * Copyright (C) 2006-2009 NEC Corporation.
7 * Module Author: Stefan Bader, IBM
8 * Modified by: Kiyoshi Ueda, NEC
10 * This file is released under the GPL.
12 * queue-length path selector - choose a path with the least number of
17 #include "dm-path-selector.h"
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>
25 #define DM_MSG_PREFIX "multipath queue-length"
27 #define QL_VERSION "0.2.0"
30 struct list_head valid_paths;
31 struct list_head failed_paths;
36 struct list_head list;
38 unsigned repeat_count;
39 atomic_t qlen; /* the number of in-flight I/Os */
42 static struct selector *alloc_selector(void)
44 struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
47 INIT_LIST_HEAD(&s->valid_paths);
48 INIT_LIST_HEAD(&s->failed_paths);
49 spin_lock_init(&s->lock);
55 static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
57 struct selector *s = alloc_selector();
66 static void ql_free_paths(struct list_head *paths)
68 struct path_info *pi, *next;
70 list_for_each_entry_safe(pi, next, paths, list) {
76 static void ql_destroy(struct path_selector *ps)
78 struct selector *s = ps->context;
80 ql_free_paths(&s->valid_paths);
81 ql_free_paths(&s->failed_paths);
86 static int ql_status(struct path_selector *ps, struct dm_path *path,
87 status_type_t type, char *result, unsigned maxlen)
92 /* When called with NULL path, return selector status/args. */
100 DMEMIT("%d ", atomic_read(&pi->qlen));
102 case STATUSTYPE_TABLE:
103 DMEMIT("%u ", pi->repeat_count);
111 static int ql_add_path(struct path_selector *ps, struct dm_path *path,
112 int argc, char **argv, char **error)
114 struct selector *s = ps->context;
115 struct path_info *pi;
116 unsigned repeat_count = QL_MIN_IO;
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.
126 *error = "queue-length ps: incorrect number of arguments";
130 if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
131 *error = "queue-length ps: invalid repeat count";
135 if (repeat_count > 1) {
136 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
140 /* Allocate the path information structure */
141 pi = kmalloc(sizeof(*pi), GFP_KERNEL);
143 *error = "queue-length ps: Error allocating path information";
148 pi->repeat_count = repeat_count;
149 atomic_set(&pi->qlen, 0);
151 path->pscontext = pi;
153 spin_lock_irqsave(&s->lock, flags);
154 list_add_tail(&pi->list, &s->valid_paths);
155 spin_unlock_irqrestore(&s->lock, flags);
160 static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
162 struct selector *s = ps->context;
163 struct path_info *pi = path->pscontext;
166 spin_lock_irqsave(&s->lock, flags);
167 list_move(&pi->list, &s->failed_paths);
168 spin_unlock_irqrestore(&s->lock, flags);
171 static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
173 struct selector *s = ps->context;
174 struct path_info *pi = path->pscontext;
177 spin_lock_irqsave(&s->lock, flags);
178 list_move_tail(&pi->list, &s->valid_paths);
179 spin_unlock_irqrestore(&s->lock, flags);
185 * Select a path having the minimum number of in-flight I/Os
187 static struct dm_path *ql_select_path(struct path_selector *ps,
188 unsigned *repeat_count, size_t nr_bytes)
190 struct selector *s = ps->context;
191 struct path_info *pi = NULL, *best = NULL;
192 struct dm_path *ret = NULL;
195 spin_lock_irqsave(&s->lock, flags);
196 if (list_empty(&s->valid_paths))
199 /* Change preferred (first in list) path to evenly balance. */
200 list_move_tail(s->valid_paths.next, &s->valid_paths);
202 list_for_each_entry(pi, &s->valid_paths, list) {
204 (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
207 if (!atomic_read(&best->qlen))
214 *repeat_count = best->repeat_count;
218 spin_unlock_irqrestore(&s->lock, flags);
222 static int ql_start_io(struct path_selector *ps, struct dm_path *path,
225 struct path_info *pi = path->pscontext;
227 atomic_inc(&pi->qlen);
232 static int ql_end_io(struct path_selector *ps, struct dm_path *path,
235 struct path_info *pi = path->pscontext;
237 atomic_dec(&pi->qlen);
242 static struct path_selector_type ql_ps = {
243 .name = "queue-length",
244 .module = THIS_MODULE,
248 .destroy = ql_destroy,
250 .add_path = ql_add_path,
251 .fail_path = ql_fail_path,
252 .reinstate_path = ql_reinstate_path,
253 .select_path = ql_select_path,
254 .start_io = ql_start_io,
258 static int __init dm_ql_init(void)
260 int r = dm_register_path_selector(&ql_ps);
263 DMERR("register failed %d", r);
265 DMINFO("version " QL_VERSION " loaded");
270 static void __exit dm_ql_exit(void)
272 int r = dm_unregister_path_selector(&ql_ps);
275 DMERR("unregister failed %d", r);
278 module_init(dm_ql_init);
279 module_exit(dm_ql_exit);
281 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
283 "(C) Copyright IBM Corp. 2004,2005 All Rights Reserved.\n"
284 DM_NAME " path selector to balance the number of in-flight I/Os"
286 MODULE_LICENSE("GPL");