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");
264
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