[go: nahoru, domu]
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