1 /*
2  * Copyright (C) 2007-2009 NEC Corporation.  All Rights Reserved.
3  *
4  * Module Author: Kiyoshi Ueda
5  *
6  * This file is released under the GPL.
7  *
8  * Throughput oriented path selector.
9  */
10 
11 #include "dm.h"
12 #include "dm-path-selector.h"
13 
14 #include <linux/slab.h>
15 #include <linux/module.h>
16 
17 #define DM_MSG_PREFIX	"multipath service-time"
18 #define ST_MIN_IO	1
19 #define ST_MAX_RELATIVE_THROUGHPUT	100
20 #define ST_MAX_RELATIVE_THROUGHPUT_SHIFT	7
21 #define ST_MAX_INFLIGHT_SIZE	((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
22 #define ST_VERSION	"0.3.0"
23 
24 struct selector {
25 	struct list_head valid_paths;
26 	struct list_head failed_paths;
27 	spinlock_t lock;
28 };
29 
30 struct path_info {
31 	struct list_head list;
32 	struct dm_path *path;
33 	unsigned repeat_count;
34 	unsigned relative_throughput;
35 	atomic_t in_flight_size;	/* Total size of in-flight I/Os */
36 };
37 
38 static struct selector *alloc_selector(void)
39 {
40 	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
41 
42 	if (s) {
43 		INIT_LIST_HEAD(&s->valid_paths);
44 		INIT_LIST_HEAD(&s->failed_paths);
45 		spin_lock_init(&s->lock);
46 	}
47 
48 	return s;
49 }
50 
51 static int st_create(struct path_selector *ps, unsigned argc, char **argv)
52 {
53 	struct selector *s = alloc_selector();
54 
55 	if (!s)
56 		return -ENOMEM;
57 
58 	ps->context = s;
59 	return 0;
60 }
61 
62 static void free_paths(struct list_head *paths)
63 {
64 	struct path_info *pi, *next;
65 
66 	list_for_each_entry_safe(pi, next, paths, list) {
67 		list_del(&pi->list);
68 		kfree(pi);
69 	}
70 }
71 
72 static void st_destroy(struct path_selector *ps)
73 {
74 	struct selector *s = ps->context;
75 
76 	free_paths(&s->valid_paths);
77 	free_paths(&s->failed_paths);
78 	kfree(s);
79 	ps->context = NULL;
80 }
81 
82 static int st_status(struct path_selector *ps, struct dm_path *path,
83 		     status_type_t type, char *result, unsigned maxlen)
84 {
85 	unsigned sz = 0;
86 	struct path_info *pi;
87 
88 	if (!path)
89 		DMEMIT("0 ");
90 	else {
91 		pi = path->pscontext;
92 
93 		switch (type) {
94 		case STATUSTYPE_INFO:
95 			DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
96 			       pi->relative_throughput);
97 			break;
98 		case STATUSTYPE_TABLE:
99 			DMEMIT("%u %u ", pi->repeat_count,
100 			       pi->relative_throughput);
101 			break;
102 		}
103 	}
104 
105 	return sz;
106 }
107 
108 static int st_add_path(struct path_selector *ps, struct dm_path *path,
109 		       int argc, char **argv, char **error)
110 {
111 	struct selector *s = ps->context;
112 	struct path_info *pi;
113 	unsigned repeat_count = ST_MIN_IO;
114 	unsigned relative_throughput = 1;
115 	char dummy;
116 	unsigned long flags;
117 
118 	/*
119 	 * Arguments: [<repeat_count> [<relative_throughput>]]
120 	 * 	<repeat_count>: The number of I/Os before switching path.
121 	 * 			If not given, default (ST_MIN_IO) is used.
122 	 * 	<relative_throughput>: The relative throughput value of
123 	 *			the path among all paths in the path-group.
124 	 * 			The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
125 	 *			If not given, minimum value '1' is used.
126 	 *			If '0' is given, the path isn't selected while
127 	 * 			other paths having a positive value are
128 	 * 			available.
129 	 */
130 	if (argc > 2) {
131 		*error = "service-time ps: incorrect number of arguments";
132 		return -EINVAL;
133 	}
134 
135 	if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
136 		*error = "service-time ps: invalid repeat count";
137 		return -EINVAL;
138 	}
139 
140 	if (repeat_count > 1) {
141 		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
142 		repeat_count = 1;
143 	}
144 
145 	if ((argc == 2) &&
146 	    (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
147 	     relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
148 		*error = "service-time ps: invalid relative_throughput value";
149 		return -EINVAL;
150 	}
151 
152 	/* allocate the path */
153 	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
154 	if (!pi) {
155 		*error = "service-time ps: Error allocating path context";
156 		return -ENOMEM;
157 	}
158 
159 	pi->path = path;
160 	pi->repeat_count = repeat_count;
161 	pi->relative_throughput = relative_throughput;
162 	atomic_set(&pi->in_flight_size, 0);
163 
164 	path->pscontext = pi;
165 
166 	spin_lock_irqsave(&s->lock, flags);
167 	list_add_tail(&pi->list, &s->valid_paths);
168 	spin_unlock_irqrestore(&s->lock, flags);
169 
170 	return 0;
171 }
172 
173 static void st_fail_path(struct path_selector *ps, struct dm_path *path)
174 {
175 	struct selector *s = ps->context;
176 	struct path_info *pi = path->pscontext;
177 	unsigned long flags;
178 
179 	spin_lock_irqsave(&s->lock, flags);
180 	list_move(&pi->list, &s->failed_paths);
181 	spin_unlock_irqrestore(&s->lock, flags);
182 }
183 
184 static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
185 {
186 	struct selector *s = ps->context;
187 	struct path_info *pi = path->pscontext;
188 	unsigned long flags;
189 
190 	spin_lock_irqsave(&s->lock, flags);
191 	list_move_tail(&pi->list, &s->valid_paths);
192 	spin_unlock_irqrestore(&s->lock, flags);
193 
194 	return 0;
195 }
196 
197 /*
198  * Compare the estimated service time of 2 paths, pi1 and pi2,
199  * for the incoming I/O.
200  *
201  * Returns:
202  * < 0 : pi1 is better
203  * 0   : no difference between pi1 and pi2
204  * > 0 : pi2 is better
205  *
206  * Description:
207  * Basically, the service time is estimated by:
208  *     ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
209  * To reduce the calculation, some optimizations are made.
210  * (See comments inline)
211  */
212 static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
213 			   size_t incoming)
214 {
215 	size_t sz1, sz2, st1, st2;
216 
217 	sz1 = atomic_read(&pi1->in_flight_size);
218 	sz2 = atomic_read(&pi2->in_flight_size);
219 
220 	/*
221 	 * Case 1: Both have same throughput value. Choose less loaded path.
222 	 */
223 	if (pi1->relative_throughput == pi2->relative_throughput)
224 		return sz1 - sz2;
225 
226 	/*
227 	 * Case 2a: Both have same load. Choose higher throughput path.
228 	 * Case 2b: One path has no throughput value. Choose the other one.
229 	 */
230 	if (sz1 == sz2 ||
231 	    !pi1->relative_throughput || !pi2->relative_throughput)
232 		return pi2->relative_throughput - pi1->relative_throughput;
233 
234 	/*
235 	 * Case 3: Calculate service time. Choose faster path.
236 	 *         Service time using pi1:
237 	 *             st1 = (sz1 + incoming) / pi1->relative_throughput
238 	 *         Service time using pi2:
239 	 *             st2 = (sz2 + incoming) / pi2->relative_throughput
240 	 *
241 	 *         To avoid the division, transform the expression to use
242 	 *         multiplication.
243 	 *         Because ->relative_throughput > 0 here, if st1 < st2,
244 	 *         the expressions below are the same meaning:
245 	 *             (sz1 + incoming) / pi1->relative_throughput <
246 	 *                 (sz2 + incoming) / pi2->relative_throughput
247 	 *             (sz1 + incoming) * pi2->relative_throughput <
248 	 *                 (sz2 + incoming) * pi1->relative_throughput
249 	 *         So use the later one.
250 	 */
251 	sz1 += incoming;
252 	sz2 += incoming;
253 	if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
254 		     sz2 >= ST_MAX_INFLIGHT_SIZE)) {
255 		/*
256 		 * Size may be too big for multiplying pi->relative_throughput
257 		 * and overflow.
258 		 * To avoid the overflow and mis-selection, shift down both.
259 		 */
260 		sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
261 		sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
262 	}
263 	st1 = sz1 * pi2->relative_throughput;
264 	st2 = sz2 * pi1->relative_throughput;
265 	if (st1 != st2)
266 		return st1 - st2;
267 
268 	/*
269 	 * Case 4: Service time is equal. Choose higher throughput path.
270 	 */
271 	return pi2->relative_throughput - pi1->relative_throughput;
272 }
273 
274 static struct dm_path *st_select_path(struct path_selector *ps, size_t nr_bytes)
275 {
276 	struct selector *s = ps->context;
277 	struct path_info *pi = NULL, *best = NULL;
278 	struct dm_path *ret = NULL;
279 	unsigned long flags;
280 
281 	spin_lock_irqsave(&s->lock, flags);
282 	if (list_empty(&s->valid_paths))
283 		goto out;
284 
285 	list_for_each_entry(pi, &s->valid_paths, list)
286 		if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
287 			best = pi;
288 
289 	if (!best)
290 		goto out;
291 
292 	/* Move most recently used to least preferred to evenly balance. */
293 	list_move_tail(&best->list, &s->valid_paths);
294 
295 	ret = best->path;
296 out:
297 	spin_unlock_irqrestore(&s->lock, flags);
298 	return ret;
299 }
300 
301 static int st_start_io(struct path_selector *ps, struct dm_path *path,
302 		       size_t nr_bytes)
303 {
304 	struct path_info *pi = path->pscontext;
305 
306 	atomic_add(nr_bytes, &pi->in_flight_size);
307 
308 	return 0;
309 }
310 
311 static int st_end_io(struct path_selector *ps, struct dm_path *path,
312 		     size_t nr_bytes, u64 start_time)
313 {
314 	struct path_info *pi = path->pscontext;
315 
316 	atomic_sub(nr_bytes, &pi->in_flight_size);
317 
318 	return 0;
319 }
320 
321 static struct path_selector_type st_ps = {
322 	.name		= "service-time",
323 	.module		= THIS_MODULE,
324 	.table_args	= 2,
325 	.info_args	= 2,
326 	.create		= st_create,
327 	.destroy	= st_destroy,
328 	.status		= st_status,
329 	.add_path	= st_add_path,
330 	.fail_path	= st_fail_path,
331 	.reinstate_path	= st_reinstate_path,
332 	.select_path	= st_select_path,
333 	.start_io	= st_start_io,
334 	.end_io		= st_end_io,
335 };
336 
337 static int __init dm_st_init(void)
338 {
339 	int r = dm_register_path_selector(&st_ps);
340 
341 	if (r < 0)
342 		DMERR("register failed %d", r);
343 
344 	DMINFO("version " ST_VERSION " loaded");
345 
346 	return r;
347 }
348 
349 static void __exit dm_st_exit(void)
350 {
351 	int r = dm_unregister_path_selector(&st_ps);
352 
353 	if (r < 0)
354 		DMERR("unregister failed %d", r);
355 }
356 
357 module_init(dm_st_init);
358 module_exit(dm_st_exit);
359 
360 MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
361 MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
362 MODULE_LICENSE("GPL");
363