summaryrefslogtreecommitdiff
path: root/drivers/md/dm-queue-length.c
blob: 51d82290ad4c6d25ef2c52d599e3f88f6c96e934 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
/*
 * Copyright (C) 2004-2005 IBM Corp.  All Rights Reserved.
 * Copyright (C) 2006-2009 NEC Corporation.
 *
 * dm-queue-length.c
 *
 * Module Author: Stefan Bader, IBM
 * Modified by: Kiyoshi Ueda, NEC
 *
 * This file is released under the GPL.
 *
 * queue-length path selector - choose a path with the least number of
 * in-flight I/Os.
 */

#include "dm.h"
#include "dm-path-selector.h"

#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/atomic.h>

#define DM_MSG_PREFIX	"multipath queue-length"
#define QL_MIN_IO	1
#define QL_VERSION	"0.2.0"

struct selector {
	struct list_head	valid_paths;
	struct list_head	failed_paths;
};

struct path_info {
	struct list_head	list;
	struct dm_path		*path;
	unsigned		repeat_count;
	atomic_t		qlen;	/* the number of in-flight I/Os */
};

static struct selector *alloc_selector(void)
{
	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);

	if (s) {
		INIT_LIST_HEAD(&s->valid_paths);
		INIT_LIST_HEAD(&s->failed_paths);
	}

	return s;
}

static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
{
	struct selector *s = alloc_selector();

	if (!s)
		return -ENOMEM;

	ps->context = s;
	return 0;
}

static void ql_free_paths(struct list_head *paths)
{
	struct path_info *pi, *next;

	list_for_each_entry_safe(pi, next, paths, list) {
		list_del(&pi->list);
		kfree(pi);
	}
}

static void ql_destroy(struct path_selector *ps)
{
	struct selector *s = ps->context;

	ql_free_paths(&s->valid_paths);
	ql_free_paths(&s->failed_paths);
	kfree(s);
	ps->context = NULL;
}

static int ql_status(struct path_selector *ps, struct dm_path *path,
		     status_type_t type, char *result, unsigned maxlen)
{
	unsigned sz = 0;
	struct path_info *pi;

	/* When called with NULL path, return selector status/args. */
	if (!path)
		DMEMIT("0 ");
	else {
		pi = path->pscontext;

		switch (type) {
		case STATUSTYPE_INFO:
			DMEMIT("%d ", atomic_read(&pi->qlen));
			break;
		case STATUSTYPE_TABLE:
			DMEMIT("%u ", pi->repeat_count);
			break;
		}
	}

	return sz;
}

static int ql_add_path(struct path_selector *ps, struct dm_path *path,
		       int argc, char **argv, char **error)
{
	struct selector *s = ps->context;
	struct path_info *pi;
	unsigned repeat_count = QL_MIN_IO;
	char dummy;

	/*
	 * Arguments: [<repeat_count>]
	 * 	<repeat_count>: The number of I/Os before switching path.
	 * 			If not given, default (QL_MIN_IO) is used.
	 */
	if (argc > 1) {
		*error = "queue-length ps: incorrect number of arguments";
		return -EINVAL;
	}

	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
		*error = "queue-length ps: invalid repeat count";
		return -EINVAL;
	}

	if (repeat_count > 1) {
		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
		repeat_count = 1;
	}

	/* Allocate the path information structure */
	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
	if (!pi) {
		*error = "queue-length ps: Error allocating path information";
		return -ENOMEM;
	}

	pi->path = path;
	pi->repeat_count = repeat_count;
	atomic_set(&pi->qlen, 0);

	path->pscontext = pi;

	list_add_tail(&pi->list, &s->valid_paths);

	return 0;
}

static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
{
	struct selector *s = ps->context;
	struct path_info *pi = path->pscontext;

	list_move(&pi->list, &s->failed_paths);
}

static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
{
	struct selector *s = ps->context;
	struct path_info *pi = path->pscontext;

	list_move_tail(&pi->list, &s->valid_paths);

	return 0;
}

/*
 * Select a path having the minimum number of in-flight I/Os
 */
static struct dm_path *ql_select_path(struct path_selector *ps,
				      unsigned *repeat_count, size_t nr_bytes)
{
	struct selector *s = ps->context;
	struct path_info *pi = NULL, *best = NULL;

	if (list_empty(&s->valid_paths))
		return NULL;

	/* Change preferred (first in list) path to evenly balance. */
	list_move_tail(s->valid_paths.next, &s->valid_paths);

	list_for_each_entry(pi, &s->valid_paths, list) {
		if (!best ||
		    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
			best = pi;

		if (!atomic_read(&best->qlen))
			break;
	}

	if (!best)
		return NULL;

	*repeat_count = best->repeat_count;

	return best->path;
}

static int ql_start_io(struct path_selector *ps, struct dm_path *path,
		       size_t nr_bytes)
{
	struct path_info *pi = path->pscontext;

	atomic_inc(&pi->qlen);

	return 0;
}

static int ql_end_io(struct path_selector *ps, struct dm_path *path,
		     size_t nr_bytes)
{
	struct path_info *pi = path->pscontext;

	atomic_dec(&pi->qlen);

	return 0;
}

static struct path_selector_type ql_ps = {
	.name		= "queue-length",
	.module		= THIS_MODULE,
	.table_args	= 1,
	.info_args	= 1,
	.create		= ql_create,
	.destroy	= ql_destroy,
	.status		= ql_status,
	.add_path	= ql_add_path,
	.fail_path	= ql_fail_path,
	.reinstate_path	= ql_reinstate_path,
	.select_path	= ql_select_path,
	.start_io	= ql_start_io,
	.end_io		= ql_end_io,
};

static int __init dm_ql_init(void)
{
	int r = dm_register_path_selector(&ql_ps);

	if (r < 0)
		DMERR("register failed %d", r);

	DMINFO("version " QL_VERSION " loaded");

	return r;
}

static void __exit dm_ql_exit(void)
{
	int r = dm_unregister_path_selector(&ql_ps);

	if (r < 0)
		DMERR("unregister failed %d", r);
}

module_init(dm_ql_init);
module_exit(dm_ql_exit);

MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
MODULE_DESCRIPTION(
	"(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
	DM_NAME " path selector to balance the number of in-flight I/Os"
);
MODULE_LICENSE("GPL");