Root/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
29struct selector {
30    struct list_head valid_paths;
31    struct list_head failed_paths;
32};
33
34struct 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
41static 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
53static 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
64static 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
74static 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
84static 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
109static 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
150static 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
158static 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 */
171static 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
200static 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
210static 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
220static 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
236static 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
248static 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
256module_init(dm_ql_init);
257module_exit(dm_ql_exit);
258
259MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
260MODULE_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);
264MODULE_LICENSE("GPL");
265

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive