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 "0.1.0"
30 struct list_head valid_paths
;
31 struct list_head failed_paths
;
35 struct list_head list
;
37 unsigned repeat_count
;
38 atomic_t qlen
; /* the number of in-flight I/Os */
41 static struct selector
*alloc_selector(void)
43 struct selector
*s
= kmalloc(sizeof(*s
), GFP_KERNEL
);
46 INIT_LIST_HEAD(&s
->valid_paths
);
47 INIT_LIST_HEAD(&s
->failed_paths
);
53 static int ql_create(struct path_selector
*ps
, unsigned argc
, char **argv
)
55 struct selector
*s
= alloc_selector();
64 static void ql_free_paths(struct list_head
*paths
)
66 struct path_info
*pi
, *next
;
68 list_for_each_entry_safe(pi
, next
, paths
, list
) {
74 static void ql_destroy(struct path_selector
*ps
)
76 struct selector
*s
= ps
->context
;
78 ql_free_paths(&s
->valid_paths
);
79 ql_free_paths(&s
->failed_paths
);
84 static int ql_status(struct path_selector
*ps
, struct dm_path
*path
,
85 status_type_t type
, char *result
, unsigned maxlen
)
90 /* When called with NULL path, return selector status/args. */
98 DMEMIT("%d ", atomic_read(&pi
->qlen
));
100 case STATUSTYPE_TABLE
:
101 DMEMIT("%u ", pi
->repeat_count
);
109 static int ql_add_path(struct path_selector
*ps
, struct dm_path
*path
,
110 int argc
, char **argv
, char **error
)
112 struct selector
*s
= ps
->context
;
113 struct path_info
*pi
;
114 unsigned repeat_count
= QL_MIN_IO
;
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.
123 *error
= "queue-length ps: incorrect number of arguments";
127 if ((argc
== 1) && (sscanf(argv
[0], "%u%c", &repeat_count
, &dummy
) != 1)) {
128 *error
= "queue-length ps: invalid repeat count";
132 /* Allocate the path information structure */
133 pi
= kmalloc(sizeof(*pi
), GFP_KERNEL
);
135 *error
= "queue-length ps: Error allocating path information";
140 pi
->repeat_count
= repeat_count
;
141 atomic_set(&pi
->qlen
, 0);
143 path
->pscontext
= pi
;
145 list_add_tail(&pi
->list
, &s
->valid_paths
);
150 static void ql_fail_path(struct path_selector
*ps
, struct dm_path
*path
)
152 struct selector
*s
= ps
->context
;
153 struct path_info
*pi
= path
->pscontext
;
155 list_move(&pi
->list
, &s
->failed_paths
);
158 static int ql_reinstate_path(struct path_selector
*ps
, struct dm_path
*path
)
160 struct selector
*s
= ps
->context
;
161 struct path_info
*pi
= path
->pscontext
;
163 list_move_tail(&pi
->list
, &s
->valid_paths
);
169 * Select a path having the minimum number of in-flight I/Os
171 static struct dm_path
*ql_select_path(struct path_selector
*ps
,
172 unsigned *repeat_count
, size_t nr_bytes
)
174 struct selector
*s
= ps
->context
;
175 struct path_info
*pi
= NULL
, *best
= NULL
;
177 if (list_empty(&s
->valid_paths
))
180 /* Change preferred (first in list) path to evenly balance. */
181 list_move_tail(s
->valid_paths
.next
, &s
->valid_paths
);
183 list_for_each_entry(pi
, &s
->valid_paths
, list
) {
185 (atomic_read(&pi
->qlen
) < atomic_read(&best
->qlen
)))
188 if (!atomic_read(&best
->qlen
))
195 *repeat_count
= best
->repeat_count
;
200 static int ql_start_io(struct path_selector
*ps
, struct dm_path
*path
,
203 struct path_info
*pi
= path
->pscontext
;
205 atomic_inc(&pi
->qlen
);
210 static int ql_end_io(struct path_selector
*ps
, struct dm_path
*path
,
213 struct path_info
*pi
= path
->pscontext
;
215 atomic_dec(&pi
->qlen
);
220 static struct path_selector_type ql_ps
= {
221 .name
= "queue-length",
222 .module
= THIS_MODULE
,
226 .destroy
= ql_destroy
,
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
,
236 static int __init
dm_ql_init(void)
238 int r
= dm_register_path_selector(&ql_ps
);
241 DMERR("register failed %d", r
);
243 DMINFO("version " QL_VERSION
" loaded");
248 static void __exit
dm_ql_exit(void)
250 int r
= dm_unregister_path_selector(&ql_ps
);
253 DMERR("unregister failed %d", r
);
256 module_init(dm_ql_init
);
257 module_exit(dm_ql_exit
);
259 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
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"
264 MODULE_LICENSE("GPL");
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