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
alloc_selector(void)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
st_create(struct path_selector * ps,unsigned argc,char ** argv)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
free_paths(struct list_head * paths)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
st_destroy(struct path_selector * ps)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
st_status(struct path_selector * ps,struct dm_path * path,status_type_t type,char * result,unsigned maxlen)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 case STATUSTYPE_IMA:
103 result[0] = '\0';
104 break;
105 }
106 }
107
108 return sz;
109 }
110
st_add_path(struct path_selector * ps,struct dm_path * path,int argc,char ** argv,char ** error)111 static int st_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 = ST_MIN_IO;
117 unsigned relative_throughput = 1;
118 char dummy;
119 unsigned long flags;
120
121 /*
122 * Arguments: [<repeat_count> [<relative_throughput>]]
123 * <repeat_count>: The number of I/Os before switching path.
124 * If not given, default (ST_MIN_IO) is used.
125 * <relative_throughput>: The relative throughput value of
126 * the path among all paths in the path-group.
127 * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
128 * If not given, minimum value '1' is used.
129 * If '0' is given, the path isn't selected while
130 * other paths having a positive value are
131 * available.
132 */
133 if (argc > 2) {
134 *error = "service-time ps: incorrect number of arguments";
135 return -EINVAL;
136 }
137
138 if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
139 *error = "service-time ps: invalid repeat count";
140 return -EINVAL;
141 }
142
143 if (repeat_count > 1) {
144 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
145 repeat_count = 1;
146 }
147
148 if ((argc == 2) &&
149 (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
150 relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
151 *error = "service-time ps: invalid relative_throughput value";
152 return -EINVAL;
153 }
154
155 /* allocate the path */
156 pi = kmalloc(sizeof(*pi), GFP_KERNEL);
157 if (!pi) {
158 *error = "service-time ps: Error allocating path context";
159 return -ENOMEM;
160 }
161
162 pi->path = path;
163 pi->repeat_count = repeat_count;
164 pi->relative_throughput = relative_throughput;
165 atomic_set(&pi->in_flight_size, 0);
166
167 path->pscontext = pi;
168
169 spin_lock_irqsave(&s->lock, flags);
170 list_add_tail(&pi->list, &s->valid_paths);
171 spin_unlock_irqrestore(&s->lock, flags);
172
173 return 0;
174 }
175
st_fail_path(struct path_selector * ps,struct dm_path * path)176 static void st_fail_path(struct path_selector *ps, struct dm_path *path)
177 {
178 struct selector *s = ps->context;
179 struct path_info *pi = path->pscontext;
180 unsigned long flags;
181
182 spin_lock_irqsave(&s->lock, flags);
183 list_move(&pi->list, &s->failed_paths);
184 spin_unlock_irqrestore(&s->lock, flags);
185 }
186
st_reinstate_path(struct path_selector * ps,struct dm_path * path)187 static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
188 {
189 struct selector *s = ps->context;
190 struct path_info *pi = path->pscontext;
191 unsigned long flags;
192
193 spin_lock_irqsave(&s->lock, flags);
194 list_move_tail(&pi->list, &s->valid_paths);
195 spin_unlock_irqrestore(&s->lock, flags);
196
197 return 0;
198 }
199
200 /*
201 * Compare the estimated service time of 2 paths, pi1 and pi2,
202 * for the incoming I/O.
203 *
204 * Returns:
205 * < 0 : pi1 is better
206 * 0 : no difference between pi1 and pi2
207 * > 0 : pi2 is better
208 *
209 * Description:
210 * Basically, the service time is estimated by:
211 * ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
212 * To reduce the calculation, some optimizations are made.
213 * (See comments inline)
214 */
st_compare_load(struct path_info * pi1,struct path_info * pi2,size_t incoming)215 static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
216 size_t incoming)
217 {
218 size_t sz1, sz2, st1, st2;
219
220 sz1 = atomic_read(&pi1->in_flight_size);
221 sz2 = atomic_read(&pi2->in_flight_size);
222
223 /*
224 * Case 1: Both have same throughput value. Choose less loaded path.
225 */
226 if (pi1->relative_throughput == pi2->relative_throughput)
227 return sz1 - sz2;
228
229 /*
230 * Case 2a: Both have same load. Choose higher throughput path.
231 * Case 2b: One path has no throughput value. Choose the other one.
232 */
233 if (sz1 == sz2 ||
234 !pi1->relative_throughput || !pi2->relative_throughput)
235 return pi2->relative_throughput - pi1->relative_throughput;
236
237 /*
238 * Case 3: Calculate service time. Choose faster path.
239 * Service time using pi1:
240 * st1 = (sz1 + incoming) / pi1->relative_throughput
241 * Service time using pi2:
242 * st2 = (sz2 + incoming) / pi2->relative_throughput
243 *
244 * To avoid the division, transform the expression to use
245 * multiplication.
246 * Because ->relative_throughput > 0 here, if st1 < st2,
247 * the expressions below are the same meaning:
248 * (sz1 + incoming) / pi1->relative_throughput <
249 * (sz2 + incoming) / pi2->relative_throughput
250 * (sz1 + incoming) * pi2->relative_throughput <
251 * (sz2 + incoming) * pi1->relative_throughput
252 * So use the later one.
253 */
254 sz1 += incoming;
255 sz2 += incoming;
256 if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
257 sz2 >= ST_MAX_INFLIGHT_SIZE)) {
258 /*
259 * Size may be too big for multiplying pi->relative_throughput
260 * and overflow.
261 * To avoid the overflow and mis-selection, shift down both.
262 */
263 sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
264 sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
265 }
266 st1 = sz1 * pi2->relative_throughput;
267 st2 = sz2 * pi1->relative_throughput;
268 if (st1 != st2)
269 return st1 - st2;
270
271 /*
272 * Case 4: Service time is equal. Choose higher throughput path.
273 */
274 return pi2->relative_throughput - pi1->relative_throughput;
275 }
276
st_select_path(struct path_selector * ps,size_t nr_bytes)277 static struct dm_path *st_select_path(struct path_selector *ps, size_t nr_bytes)
278 {
279 struct selector *s = ps->context;
280 struct path_info *pi = NULL, *best = NULL;
281 struct dm_path *ret = NULL;
282 unsigned long flags;
283
284 spin_lock_irqsave(&s->lock, flags);
285 if (list_empty(&s->valid_paths))
286 goto out;
287
288 list_for_each_entry(pi, &s->valid_paths, list)
289 if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
290 best = pi;
291
292 if (!best)
293 goto out;
294
295 /* Move most recently used to least preferred to evenly balance. */
296 list_move_tail(&best->list, &s->valid_paths);
297
298 ret = best->path;
299 out:
300 spin_unlock_irqrestore(&s->lock, flags);
301 return ret;
302 }
303
st_start_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes)304 static int st_start_io(struct path_selector *ps, struct dm_path *path,
305 size_t nr_bytes)
306 {
307 struct path_info *pi = path->pscontext;
308
309 atomic_add(nr_bytes, &pi->in_flight_size);
310
311 return 0;
312 }
313
st_end_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes,u64 start_time)314 static int st_end_io(struct path_selector *ps, struct dm_path *path,
315 size_t nr_bytes, u64 start_time)
316 {
317 struct path_info *pi = path->pscontext;
318
319 atomic_sub(nr_bytes, &pi->in_flight_size);
320
321 return 0;
322 }
323
324 static struct path_selector_type st_ps = {
325 .name = "service-time",
326 .module = THIS_MODULE,
327 .table_args = 2,
328 .info_args = 2,
329 .create = st_create,
330 .destroy = st_destroy,
331 .status = st_status,
332 .add_path = st_add_path,
333 .fail_path = st_fail_path,
334 .reinstate_path = st_reinstate_path,
335 .select_path = st_select_path,
336 .start_io = st_start_io,
337 .end_io = st_end_io,
338 };
339
dm_st_init(void)340 static int __init dm_st_init(void)
341 {
342 int r = dm_register_path_selector(&st_ps);
343
344 if (r < 0)
345 DMERR("register failed %d", r);
346
347 DMINFO("version " ST_VERSION " loaded");
348
349 return r;
350 }
351
dm_st_exit(void)352 static void __exit dm_st_exit(void)
353 {
354 int r = dm_unregister_path_selector(&st_ps);
355
356 if (r < 0)
357 DMERR("unregister failed %d", r);
358 }
359
360 module_init(dm_st_init);
361 module_exit(dm_st_exit);
362
363 MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
364 MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
365 MODULE_LICENSE("GPL");
366
