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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"); |