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/drivers/md/dm-queue-length.c

http://github.com/mirrors/linux
C | 283 lines | 203 code | 55 blank | 25 comment | 18 complexity | d0da88f4c1324001c97f0260167c02f6 MD5 | raw file
  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	1
 27#define QL_VERSION	"0.2.0"
 28
 29struct selector {
 30	struct list_head	valid_paths;
 31	struct list_head	failed_paths;
 32	spinlock_t lock;
 33};
 34
 35struct path_info {
 36	struct list_head	list;
 37	struct dm_path		*path;
 38	unsigned		repeat_count;
 39	atomic_t		qlen;	/* the number of in-flight I/Os */
 40};
 41
 42static struct selector *alloc_selector(void)
 43{
 44	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
 45
 46	if (s) {
 47		INIT_LIST_HEAD(&s->valid_paths);
 48		INIT_LIST_HEAD(&s->failed_paths);
 49		spin_lock_init(&s->lock);
 50	}
 51
 52	return s;
 53}
 54
 55static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
 56{
 57	struct selector *s = alloc_selector();
 58
 59	if (!s)
 60		return -ENOMEM;
 61
 62	ps->context = s;
 63	return 0;
 64}
 65
 66static void ql_free_paths(struct list_head *paths)
 67{
 68	struct path_info *pi, *next;
 69
 70	list_for_each_entry_safe(pi, next, paths, list) {
 71		list_del(&pi->list);
 72		kfree(pi);
 73	}
 74}
 75
 76static void ql_destroy(struct path_selector *ps)
 77{
 78	struct selector *s = ps->context;
 79
 80	ql_free_paths(&s->valid_paths);
 81	ql_free_paths(&s->failed_paths);
 82	kfree(s);
 83	ps->context = NULL;
 84}
 85
 86static int ql_status(struct path_selector *ps, struct dm_path *path,
 87		     status_type_t type, char *result, unsigned maxlen)
 88{
 89	unsigned sz = 0;
 90	struct path_info *pi;
 91
 92	/* When called with NULL path, return selector status/args. */
 93	if (!path)
 94		DMEMIT("0 ");
 95	else {
 96		pi = path->pscontext;
 97
 98		switch (type) {
 99		case STATUSTYPE_INFO:
100			DMEMIT("%d ", atomic_read(&pi->qlen));
101			break;
102		case STATUSTYPE_TABLE:
103			DMEMIT("%u ", pi->repeat_count);
104			break;
105		}
106	}
107
108	return sz;
109}
110
111static int ql_add_path(struct path_selector *ps, struct dm_path *path,
112		       int argc, char **argv, char **error)
113{
114	struct selector *s = ps->context;
115	struct path_info *pi;
116	unsigned repeat_count = QL_MIN_IO;
117	char dummy;
118	unsigned long flags;
119
120	/*
121	 * Arguments: [<repeat_count>]
122	 * 	<repeat_count>: The number of I/Os before switching path.
123	 * 			If not given, default (QL_MIN_IO) is used.
124	 */
125	if (argc > 1) {
126		*error = "queue-length ps: incorrect number of arguments";
127		return -EINVAL;
128	}
129
130	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
131		*error = "queue-length ps: invalid repeat count";
132		return -EINVAL;
133	}
134
135	if (repeat_count > 1) {
136		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
137		repeat_count = 1;
138	}
139
140	/* Allocate the path information structure */
141	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
142	if (!pi) {
143		*error = "queue-length ps: Error allocating path information";
144		return -ENOMEM;
145	}
146
147	pi->path = path;
148	pi->repeat_count = repeat_count;
149	atomic_set(&pi->qlen, 0);
150
151	path->pscontext = pi;
152
153	spin_lock_irqsave(&s->lock, flags);
154	list_add_tail(&pi->list, &s->valid_paths);
155	spin_unlock_irqrestore(&s->lock, flags);
156
157	return 0;
158}
159
160static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
161{
162	struct selector *s = ps->context;
163	struct path_info *pi = path->pscontext;
164	unsigned long flags;
165
166	spin_lock_irqsave(&s->lock, flags);
167	list_move(&pi->list, &s->failed_paths);
168	spin_unlock_irqrestore(&s->lock, flags);
169}
170
171static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
172{
173	struct selector *s = ps->context;
174	struct path_info *pi = path->pscontext;
175	unsigned long flags;
176
177	spin_lock_irqsave(&s->lock, flags);
178	list_move_tail(&pi->list, &s->valid_paths);
179	spin_unlock_irqrestore(&s->lock, flags);
180
181	return 0;
182}
183
184/*
185 * Select a path having the minimum number of in-flight I/Os
186 */
187static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes)
188{
189	struct selector *s = ps->context;
190	struct path_info *pi = NULL, *best = NULL;
191	struct dm_path *ret = NULL;
192	unsigned long flags;
193
194	spin_lock_irqsave(&s->lock, flags);
195	if (list_empty(&s->valid_paths))
196		goto out;
197
198	list_for_each_entry(pi, &s->valid_paths, list) {
199		if (!best ||
200		    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
201			best = pi;
202
203		if (!atomic_read(&best->qlen))
204			break;
205	}
206
207	if (!best)
208		goto out;
209
210	/* Move most recently used to least preferred to evenly balance. */
211	list_move_tail(&best->list, &s->valid_paths);
212
213	ret = best->path;
214out:
215	spin_unlock_irqrestore(&s->lock, flags);
216	return ret;
217}
218
219static int ql_start_io(struct path_selector *ps, struct dm_path *path,
220		       size_t nr_bytes)
221{
222	struct path_info *pi = path->pscontext;
223
224	atomic_inc(&pi->qlen);
225
226	return 0;
227}
228
229static int ql_end_io(struct path_selector *ps, struct dm_path *path,
230		     size_t nr_bytes)
231{
232	struct path_info *pi = path->pscontext;
233
234	atomic_dec(&pi->qlen);
235
236	return 0;
237}
238
239static struct path_selector_type ql_ps = {
240	.name		= "queue-length",
241	.module		= THIS_MODULE,
242	.table_args	= 1,
243	.info_args	= 1,
244	.create		= ql_create,
245	.destroy	= ql_destroy,
246	.status		= ql_status,
247	.add_path	= ql_add_path,
248	.fail_path	= ql_fail_path,
249	.reinstate_path	= ql_reinstate_path,
250	.select_path	= ql_select_path,
251	.start_io	= ql_start_io,
252	.end_io		= ql_end_io,
253};
254
255static int __init dm_ql_init(void)
256{
257	int r = dm_register_path_selector(&ql_ps);
258
259	if (r < 0)
260		DMERR("register failed %d", r);
261
262	DMINFO("version " QL_VERSION " loaded");
263
264	return r;
265}
266
267static void __exit dm_ql_exit(void)
268{
269	int r = dm_unregister_path_selector(&ql_ps);
270
271	if (r < 0)
272		DMERR("unregister failed %d", r);
273}
274
275module_init(dm_ql_init);
276module_exit(dm_ql_exit);
277
278MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
279MODULE_DESCRIPTION(
280	"(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
281	DM_NAME " path selector to balance the number of in-flight I/Os"
282);
283MODULE_LICENSE("GPL");