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 		}
106 	}
107 
108 	return sz;
109 }
110 
111 static 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 
160 static 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 
171 static 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  */
187 static 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;
214 out:
215 	spin_unlock_irqrestore(&s->lock, flags);
216 	return ret;
217 }
218 
219 static 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 
229 static int ql_end_io(struct path_selector *ps, struct dm_path *path,
230 		     size_t nr_bytes, u64 start_time)
231 {
232 	struct path_info *pi = path->pscontext;
233 
234 	atomic_dec(&pi->qlen);
235 
236 	return 0;
237 }
238 
239 static 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 
255 static 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 
267 static 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 
275 module_init(dm_ql_init);
276 module_exit(dm_ql_exit);
277 
278 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
279 MODULE_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 );
283 MODULE_LICENSE("GPL");
284