1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (C) 2004-2005 IBM Corp.  All Rights Reserved.
  4 * Copyright (C) 2006-2009 NEC Corporation.
  5 *
  6 * dm-queue-length.c
  7 *
  8 * Module Author: Stefan Bader, IBM
  9 * Modified by: Kiyoshi Ueda, NEC
 10 *
 11 * This file is released under the GPL.
 12 *
 13 * queue-length path selector - choose a path with the least number of
 14 * in-flight I/Os.
 15 */
 16
 17#include "dm.h"
 18#include "dm-path-selector.h"
 19
 20#include <linux/slab.h>
 21#include <linux/ctype.h>
 22#include <linux/errno.h>
 23#include <linux/module.h>
 24#include <linux/atomic.h>
 25
 26#define DM_MSG_PREFIX	"multipath queue-length"
 27#define QL_MIN_IO	1
 28#define QL_VERSION	"0.2.0"
 29
 30struct selector {
 31	struct list_head	valid_paths;
 32	struct list_head	failed_paths;
 33	spinlock_t lock;
 34};
 35
 36struct path_info {
 37	struct list_head	list;
 38	struct dm_path		*path;
 39	unsigned int		repeat_count;
 40	atomic_t		qlen;	/* the number of in-flight I/Os */
 41};
 42
 43static struct selector *alloc_selector(void)
 44{
 45	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
 46
 47	if (s) {
 48		INIT_LIST_HEAD(&s->valid_paths);
 49		INIT_LIST_HEAD(&s->failed_paths);
 50		spin_lock_init(&s->lock);
 51	}
 52
 53	return s;
 54}
 55
 56static int ql_create(struct path_selector *ps, unsigned int argc, char **argv)
 57{
 58	struct selector *s = alloc_selector();
 59
 60	if (!s)
 61		return -ENOMEM;
 62
 63	ps->context = s;
 64	return 0;
 65}
 66
 67static void ql_free_paths(struct list_head *paths)
 68{
 69	struct path_info *pi, *next;
 70
 71	list_for_each_entry_safe(pi, next, paths, list) {
 72		list_del(&pi->list);
 73		kfree(pi);
 74	}
 75}
 76
 77static void ql_destroy(struct path_selector *ps)
 78{
 79	struct selector *s = ps->context;
 80
 81	ql_free_paths(&s->valid_paths);
 82	ql_free_paths(&s->failed_paths);
 83	kfree(s);
 84	ps->context = NULL;
 85}
 86
 87static int ql_status(struct path_selector *ps, struct dm_path *path,
 88		     status_type_t type, char *result, unsigned int maxlen)
 89{
 90	unsigned int sz = 0;
 91	struct path_info *pi;
 92
 93	/* When called with NULL path, return selector status/args. */
 94	if (!path)
 95		DMEMIT("0 ");
 96	else {
 97		pi = path->pscontext;
 98
 99		switch (type) {
100		case STATUSTYPE_INFO:
101			DMEMIT("%d ", atomic_read(&pi->qlen));
102			break;
103		case STATUSTYPE_TABLE:
104			DMEMIT("%u ", pi->repeat_count);
105			break;
106		case STATUSTYPE_IMA:
107			*result = '\0';
108			break;
109		}
110	}
111
112	return sz;
113}
114
115static int ql_add_path(struct path_selector *ps, struct dm_path *path,
116		       int argc, char **argv, char **error)
117{
118	struct selector *s = ps->context;
119	struct path_info *pi;
120	unsigned int repeat_count = QL_MIN_IO;
121	char dummy;
122	unsigned long flags;
123
124	/*
125	 * Arguments: [<repeat_count>]
126	 *	<repeat_count>: The number of I/Os before switching path.
127	 *			If not given, default (QL_MIN_IO) is used.
128	 */
129	if (argc > 1) {
130		*error = "queue-length ps: incorrect number of arguments";
131		return -EINVAL;
132	}
133
134	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
135		*error = "queue-length ps: invalid repeat count";
136		return -EINVAL;
137	}
138
139	if (repeat_count > 1) {
140		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
141		repeat_count = 1;
142	}
143
144	/* Allocate the path information structure */
145	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
146	if (!pi) {
147		*error = "queue-length ps: Error allocating path information";
148		return -ENOMEM;
149	}
150
151	pi->path = path;
152	pi->repeat_count = repeat_count;
153	atomic_set(&pi->qlen, 0);
154
155	path->pscontext = pi;
156
157	spin_lock_irqsave(&s->lock, flags);
158	list_add_tail(&pi->list, &s->valid_paths);
159	spin_unlock_irqrestore(&s->lock, flags);
160
161	return 0;
162}
163
164static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
165{
166	struct selector *s = ps->context;
167	struct path_info *pi = path->pscontext;
168	unsigned long flags;
169
170	spin_lock_irqsave(&s->lock, flags);
171	list_move(&pi->list, &s->failed_paths);
172	spin_unlock_irqrestore(&s->lock, flags);
173}
174
175static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
176{
177	struct selector *s = ps->context;
178	struct path_info *pi = path->pscontext;
179	unsigned long flags;
180
181	spin_lock_irqsave(&s->lock, flags);
182	list_move_tail(&pi->list, &s->valid_paths);
183	spin_unlock_irqrestore(&s->lock, flags);
184
185	return 0;
186}
187
188/*
189 * Select a path having the minimum number of in-flight I/Os
190 */
191static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes)
192{
193	struct selector *s = ps->context;
194	struct path_info *pi = NULL, *best = NULL;
195	struct dm_path *ret = NULL;
196	unsigned long flags;
197
198	spin_lock_irqsave(&s->lock, flags);
199	if (list_empty(&s->valid_paths))
200		goto out;
201
202	list_for_each_entry(pi, &s->valid_paths, list) {
203		if (!best ||
204		    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
205			best = pi;
206
207		if (!atomic_read(&best->qlen))
208			break;
209	}
210
211	if (!best)
212		goto out;
213
214	/* Move most recently used to least preferred to evenly balance. */
215	list_move_tail(&best->list, &s->valid_paths);
216
217	ret = best->path;
218out:
219	spin_unlock_irqrestore(&s->lock, flags);
220	return ret;
221}
222
223static int ql_start_io(struct path_selector *ps, struct dm_path *path,
224		       size_t nr_bytes)
225{
226	struct path_info *pi = path->pscontext;
227
228	atomic_inc(&pi->qlen);
229
230	return 0;
231}
232
233static int ql_end_io(struct path_selector *ps, struct dm_path *path,
234		     size_t nr_bytes, u64 start_time)
235{
236	struct path_info *pi = path->pscontext;
237
238	atomic_dec(&pi->qlen);
239
240	return 0;
241}
242
243static struct path_selector_type ql_ps = {
244	.name		= "queue-length",
245	.module		= THIS_MODULE,
246	.table_args	= 1,
247	.info_args	= 1,
248	.create		= ql_create,
249	.destroy	= ql_destroy,
250	.status		= ql_status,
251	.add_path	= ql_add_path,
252	.fail_path	= ql_fail_path,
253	.reinstate_path	= ql_reinstate_path,
254	.select_path	= ql_select_path,
255	.start_io	= ql_start_io,
256	.end_io		= ql_end_io,
257};
258
259static int __init dm_ql_init(void)
260{
261	int r = dm_register_path_selector(&ql_ps);
262
263	if (r < 0)
264		DMERR("register failed %d", r);
265
266	DMINFO("version " QL_VERSION " loaded");
267
268	return r;
269}
270
271static void __exit dm_ql_exit(void)
272{
273	int r = dm_unregister_path_selector(&ql_ps);
274
275	if (r < 0)
276		DMERR("unregister failed %d", r);
277}
278
279module_init(dm_ql_init);
280module_exit(dm_ql_exit);
281
282MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
283MODULE_DESCRIPTION(
284	"(C) Copyright IBM Corp. 2004,2005   All Rights Reserved.\n"
285	DM_NAME " path selector to balance the number of in-flight I/Os"
286);
287MODULE_LICENSE("GPL");