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
alloc_selector(void)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
ql_create(struct path_selector * ps,unsigned argc,char ** argv)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
ql_free_paths(struct list_head * paths)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
ql_destroy(struct path_selector * ps)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
ql_status(struct path_selector * ps,struct dm_path * path,status_type_t type,char * result,unsigned maxlen)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
ql_add_path(struct path_selector * ps,struct dm_path * path,int argc,char ** argv,char ** error)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
ql_fail_path(struct path_selector * ps,struct dm_path * path)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
ql_reinstate_path(struct path_selector * ps,struct dm_path * path)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 */
ql_select_path(struct path_selector * ps,unsigned * repeat_count,size_t nr_bytes)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
ql_start_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes)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
ql_end_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes)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
dm_ql_init(void)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
dm_ql_exit(void)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");
265