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f392ba88 KU |
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 | ||
5a0e3ad6 | 14 | #include <linux/slab.h> |
056075c7 | 15 | #include <linux/module.h> |
5a0e3ad6 | 16 | |
f392ba88 KU |
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 | ||
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 | ||
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 | ||
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 | ||
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 | ||
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 | ||
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; | |
31998ef1 | 113 | char dummy; |
f392ba88 KU |
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 | ||
31998ef1 | 132 | if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) { |
f392ba88 KU |
133 | *error = "service-time ps: invalid repeat count"; |
134 | return -EINVAL; | |
135 | } | |
136 | ||
137 | if ((argc == 2) && | |
31998ef1 | 138 | (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 || |
f392ba88 KU |
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 | ||
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 | ||
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 | */ | |
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 | ||
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 | ||
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 | ||
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 | ||
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 | ||
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"); |