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		case STATUSTYPE_IMA:
106			*result = '\0';
107			break;
108		}
109	}
110
111	return sz;
112}
113
114static int ql_add_path(struct path_selector *ps, struct dm_path *path,
115		       int argc, char **argv, char **error)
116{
117	struct selector *s = ps->context;
118	struct path_info *pi;
119	unsigned repeat_count = QL_MIN_IO;
120	char dummy;
121	unsigned long flags;
122
123	/*
124	 * Arguments: [<repeat_count>]
125	 * 	<repeat_count>: The number of I/Os before switching path.
126	 * 			If not given, default (QL_MIN_IO) is used.
127	 */
128	if (argc > 1) {
129		*error = "queue-length ps: incorrect number of arguments";
130		return -EINVAL;
131	}
132
133	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
134		*error = "queue-length ps: invalid repeat count";
135		return -EINVAL;
136	}
137
138	if (repeat_count > 1) {
139		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
140		repeat_count = 1;
141	}
142
143	/* Allocate the path information structure */
144	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
145	if (!pi) {
146		*error = "queue-length ps: Error allocating path information";
147		return -ENOMEM;
148	}
149
150	pi->path = path;
151	pi->repeat_count = repeat_count;
152	atomic_set(&pi->qlen, 0);
153
154	path->pscontext = pi;
155
156	spin_lock_irqsave(&s->lock, flags);
157	list_add_tail(&pi->list, &s->valid_paths);
158	spin_unlock_irqrestore(&s->lock, flags);
159
160	return 0;
161}
162
163static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
164{
165	struct selector *s = ps->context;
166	struct path_info *pi = path->pscontext;
167	unsigned long flags;
168
169	spin_lock_irqsave(&s->lock, flags);
170	list_move(&pi->list, &s->failed_paths);
171	spin_unlock_irqrestore(&s->lock, flags);
172}
173
174static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
175{
176	struct selector *s = ps->context;
177	struct path_info *pi = path->pscontext;
178	unsigned long flags;
179
180	spin_lock_irqsave(&s->lock, flags);
181	list_move_tail(&pi->list, &s->valid_paths);
182	spin_unlock_irqrestore(&s->lock, flags);
183
184	return 0;
185}
186
187/*
188 * Select a path having the minimum number of in-flight I/Os
189 */
190static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes)
191{
192	struct selector *s = ps->context;
193	struct path_info *pi = NULL, *best = NULL;
194	struct dm_path *ret = NULL;
195	unsigned long flags;
196
197	spin_lock_irqsave(&s->lock, flags);
198	if (list_empty(&s->valid_paths))
199		goto out;
200
201	list_for_each_entry(pi, &s->valid_paths, list) {
202		if (!best ||
203		    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
204			best = pi;
205
206		if (!atomic_read(&best->qlen))
207			break;
208	}
209
210	if (!best)
211		goto out;
212
213	/* Move most recently used to least preferred to evenly balance. */
214	list_move_tail(&best->list, &s->valid_paths);
215
216	ret = best->path;
217out:
218	spin_unlock_irqrestore(&s->lock, flags);
219	return ret;
220}
221
222static int ql_start_io(struct path_selector *ps, struct dm_path *path,
223		       size_t nr_bytes)
224{
225	struct path_info *pi = path->pscontext;
226
227	atomic_inc(&pi->qlen);
228
229	return 0;
230}
231
232static int ql_end_io(struct path_selector *ps, struct dm_path *path,
233		     size_t nr_bytes, u64 start_time)
234{
235	struct path_info *pi = path->pscontext;
236
237	atomic_dec(&pi->qlen);
238
239	return 0;
240}
241
242static struct path_selector_type ql_ps = {
243	.name		= "queue-length",
244	.module		= THIS_MODULE,
245	.table_args	= 1,
246	.info_args	= 1,
247	.create		= ql_create,
248	.destroy	= ql_destroy,
249	.status		= ql_status,
250	.add_path	= ql_add_path,
251	.fail_path	= ql_fail_path,
252	.reinstate_path	= ql_reinstate_path,
253	.select_path	= ql_select_path,
254	.start_io	= ql_start_io,
255	.end_io		= ql_end_io,
256};
257
258static int __init dm_ql_init(void)
259{
260	int r = dm_register_path_selector(&ql_ps);
261
262	if (r < 0)
263		DMERR("register failed %d", r);
264
265	DMINFO("version " QL_VERSION " loaded");
266
267	return r;
268}
269
270static void __exit dm_ql_exit(void)
271{
272	int r = dm_unregister_path_selector(&ql_ps);
273
274	if (r < 0)
275		DMERR("unregister failed %d", r);
276}
277
278module_init(dm_ql_init);
279module_exit(dm_ql_exit);
280
281MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
282MODULE_DESCRIPTION(
283	"(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
284	DM_NAME " path selector to balance the number of in-flight I/Os"
285);
286MODULE_LICENSE("GPL");