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 "0.2.0"
23
24 struct selector {
25 struct list_head valid_paths;
26 struct list_head failed_paths;
27 };
28
29 struct path_info {
30 struct list_head list;
31 struct dm_path *path;
32 unsigned repeat_count;
33 unsigned relative_throughput;
34 atomic_t in_flight_size; /* Total size of in-flight I/Os */
35 };
36
alloc_selector(void)37 static struct selector *alloc_selector(void)
38 {
39 struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
40
41 if (s) {
42 INIT_LIST_HEAD(&s->valid_paths);
43 INIT_LIST_HEAD(&s->failed_paths);
44 }
45
46 return s;
47 }
48
st_create(struct path_selector * ps,unsigned argc,char ** argv)49 static int st_create(struct path_selector *ps, unsigned argc, char **argv)
50 {
51 struct selector *s = alloc_selector();
52
53 if (!s)
54 return -ENOMEM;
55
56 ps->context = s;
57 return 0;
58 }
59
free_paths(struct list_head * paths)60 static void free_paths(struct list_head *paths)
61 {
62 struct path_info *pi, *next;
63
64 list_for_each_entry_safe(pi, next, paths, list) {
65 list_del(&pi->list);
66 kfree(pi);
67 }
68 }
69
st_destroy(struct path_selector * ps)70 static void st_destroy(struct path_selector *ps)
71 {
72 struct selector *s = ps->context;
73
74 free_paths(&s->valid_paths);
75 free_paths(&s->failed_paths);
76 kfree(s);
77 ps->context = NULL;
78 }
79
st_status(struct path_selector * ps,struct dm_path * path,status_type_t type,char * result,unsigned maxlen)80 static int st_status(struct path_selector *ps, struct dm_path *path,
81 status_type_t type, char *result, unsigned maxlen)
82 {
83 unsigned sz = 0;
84 struct path_info *pi;
85
86 if (!path)
87 DMEMIT("0 ");
88 else {
89 pi = path->pscontext;
90
91 switch (type) {
92 case STATUSTYPE_INFO:
93 DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
94 pi->relative_throughput);
95 break;
96 case STATUSTYPE_TABLE:
97 DMEMIT("%u %u ", pi->repeat_count,
98 pi->relative_throughput);
99 break;
100 }
101 }
102
103 return sz;
104 }
105
st_add_path(struct path_selector * ps,struct dm_path * path,int argc,char ** argv,char ** error)106 static int st_add_path(struct path_selector *ps, struct dm_path *path,
107 int argc, char **argv, char **error)
108 {
109 struct selector *s = ps->context;
110 struct path_info *pi;
111 unsigned repeat_count = ST_MIN_IO;
112 unsigned relative_throughput = 1;
113 char dummy;
114
115 /*
116 * Arguments: [<repeat_count> [<relative_throughput>]]
117 * <repeat_count>: The number of I/Os before switching path.
118 * If not given, default (ST_MIN_IO) is used.
119 * <relative_throughput>: The relative throughput value of
120 * the path among all paths in the path-group.
121 * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
122 * If not given, minimum value '1' is used.
123 * If '0' is given, the path isn't selected while
124 * other paths having a positive value are
125 * available.
126 */
127 if (argc > 2) {
128 *error = "service-time ps: incorrect number of arguments";
129 return -EINVAL;
130 }
131
132 if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
133 *error = "service-time ps: invalid repeat count";
134 return -EINVAL;
135 }
136
137 if ((argc == 2) &&
138 (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
139 relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
140 *error = "service-time ps: invalid relative_throughput value";
141 return -EINVAL;
142 }
143
144 /* allocate the path */
145 pi = kmalloc(sizeof(*pi), GFP_KERNEL);
146 if (!pi) {
147 *error = "service-time ps: Error allocating path context";
148 return -ENOMEM;
149 }
150
151 pi->path = path;
152 pi->repeat_count = repeat_count;
153 pi->relative_throughput = relative_throughput;
154 atomic_set(&pi->in_flight_size, 0);
155
156 path->pscontext = pi;
157
158 list_add_tail(&pi->list, &s->valid_paths);
159
160 return 0;
161 }
162
st_fail_path(struct path_selector * ps,struct dm_path * path)163 static void st_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
168 list_move(&pi->list, &s->failed_paths);
169 }
170
st_reinstate_path(struct path_selector * ps,struct dm_path * path)171 static int st_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
176 list_move_tail(&pi->list, &s->valid_paths);
177
178 return 0;
179 }
180
181 /*
182 * Compare the estimated service time of 2 paths, pi1 and pi2,
183 * for the incoming I/O.
184 *
185 * Returns:
186 * < 0 : pi1 is better
187 * 0 : no difference between pi1 and pi2
188 * > 0 : pi2 is better
189 *
190 * Description:
191 * Basically, the service time is estimated by:
192 * ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
193 * To reduce the calculation, some optimizations are made.
194 * (See comments inline)
195 */
st_compare_load(struct path_info * pi1,struct path_info * pi2,size_t incoming)196 static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
197 size_t incoming)
198 {
199 size_t sz1, sz2, st1, st2;
200
201 sz1 = atomic_read(&pi1->in_flight_size);
202 sz2 = atomic_read(&pi2->in_flight_size);
203
204 /*
205 * Case 1: Both have same throughput value. Choose less loaded path.
206 */
207 if (pi1->relative_throughput == pi2->relative_throughput)
208 return sz1 - sz2;
209
210 /*
211 * Case 2a: Both have same load. Choose higher throughput path.
212 * Case 2b: One path has no throughput value. Choose the other one.
213 */
214 if (sz1 == sz2 ||
215 !pi1->relative_throughput || !pi2->relative_throughput)
216 return pi2->relative_throughput - pi1->relative_throughput;
217
218 /*
219 * Case 3: Calculate service time. Choose faster path.
220 * Service time using pi1:
221 * st1 = (sz1 + incoming) / pi1->relative_throughput
222 * Service time using pi2:
223 * st2 = (sz2 + incoming) / pi2->relative_throughput
224 *
225 * To avoid the division, transform the expression to use
226 * multiplication.
227 * Because ->relative_throughput > 0 here, if st1 < st2,
228 * the expressions below are the same meaning:
229 * (sz1 + incoming) / pi1->relative_throughput <
230 * (sz2 + incoming) / pi2->relative_throughput
231 * (sz1 + incoming) * pi2->relative_throughput <
232 * (sz2 + incoming) * pi1->relative_throughput
233 * So use the later one.
234 */
235 sz1 += incoming;
236 sz2 += incoming;
237 if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
238 sz2 >= ST_MAX_INFLIGHT_SIZE)) {
239 /*
240 * Size may be too big for multiplying pi->relative_throughput
241 * and overflow.
242 * To avoid the overflow and mis-selection, shift down both.
243 */
244 sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
245 sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
246 }
247 st1 = sz1 * pi2->relative_throughput;
248 st2 = sz2 * pi1->relative_throughput;
249 if (st1 != st2)
250 return st1 - st2;
251
252 /*
253 * Case 4: Service time is equal. Choose higher throughput path.
254 */
255 return pi2->relative_throughput - pi1->relative_throughput;
256 }
257
st_select_path(struct path_selector * ps,unsigned * repeat_count,size_t nr_bytes)258 static struct dm_path *st_select_path(struct path_selector *ps,
259 unsigned *repeat_count, size_t nr_bytes)
260 {
261 struct selector *s = ps->context;
262 struct path_info *pi = NULL, *best = NULL;
263
264 if (list_empty(&s->valid_paths))
265 return NULL;
266
267 /* Change preferred (first in list) path to evenly balance. */
268 list_move_tail(s->valid_paths.next, &s->valid_paths);
269
270 list_for_each_entry(pi, &s->valid_paths, list)
271 if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
272 best = pi;
273
274 if (!best)
275 return NULL;
276
277 *repeat_count = best->repeat_count;
278
279 return best->path;
280 }
281
st_start_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes)282 static int st_start_io(struct path_selector *ps, struct dm_path *path,
283 size_t nr_bytes)
284 {
285 struct path_info *pi = path->pscontext;
286
287 atomic_add(nr_bytes, &pi->in_flight_size);
288
289 return 0;
290 }
291
st_end_io(struct path_selector * ps,struct dm_path * path,size_t nr_bytes)292 static int st_end_io(struct path_selector *ps, struct dm_path *path,
293 size_t nr_bytes)
294 {
295 struct path_info *pi = path->pscontext;
296
297 atomic_sub(nr_bytes, &pi->in_flight_size);
298
299 return 0;
300 }
301
302 static struct path_selector_type st_ps = {
303 .name = "service-time",
304 .module = THIS_MODULE,
305 .table_args = 2,
306 .info_args = 2,
307 .create = st_create,
308 .destroy = st_destroy,
309 .status = st_status,
310 .add_path = st_add_path,
311 .fail_path = st_fail_path,
312 .reinstate_path = st_reinstate_path,
313 .select_path = st_select_path,
314 .start_io = st_start_io,
315 .end_io = st_end_io,
316 };
317
dm_st_init(void)318 static int __init dm_st_init(void)
319 {
320 int r = dm_register_path_selector(&st_ps);
321
322 if (r < 0)
323 DMERR("register failed %d", r);
324
325 DMINFO("version " ST_VERSION " loaded");
326
327 return r;
328 }
329
dm_st_exit(void)330 static void __exit dm_st_exit(void)
331 {
332 int r = dm_unregister_path_selector(&st_ps);
333
334 if (r < 0)
335 DMERR("unregister failed %d", r);
336 }
337
338 module_init(dm_st_init);
339 module_exit(dm_st_exit);
340
341 MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
342 MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
343 MODULE_LICENSE("GPL");
344