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 
30 struct selector {
31 	struct list_head	valid_paths;
32 	struct list_head	failed_paths;
33 	spinlock_t lock;
34 };
35 
36 struct 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 
43 static 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 
56 static 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 
67 static 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 
77 static 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 
87 static 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 
115 static 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 
164 static 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 
175 static 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  */
191 static 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;
218 out:
219 	spin_unlock_irqrestore(&s->lock, flags);
220 	return ret;
221 }
222 
223 static 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 
233 static 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 
243 static 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 
259 static 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 
271 static 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 
279 module_init(dm_ql_init);
280 module_exit(dm_ql_exit);
281 
282 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
283 MODULE_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 );
287 MODULE_LICENSE("GPL");
288