i2c: tegra: Add stub runtime power management
[linux-2.6.git] / drivers / md / dm-queue-length.c
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
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");