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 
29 struct selector {
30 	struct list_head	valid_paths;
31 	struct list_head	failed_paths;
32 	spinlock_t lock;
33 };
34 
35 struct 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 
42 static 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 
55 static 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 
66 static 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 
76 static 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 
86 static 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 
114 static 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 
163 static 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 
174 static 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  */
190 static 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;
217 out:
218 	spin_unlock_irqrestore(&s->lock, flags);
219 	return ret;
220 }
221 
222 static 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 
232 static 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 
242 static 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 
258 static 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 
270 static 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 
278 module_init(dm_ql_init);
279 module_exit(dm_ql_exit);
280 
281 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
282 MODULE_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 );
286 MODULE_LICENSE("GPL");
287