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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 | ||
14 | #define DM_MSG_PREFIX "multipath service-time" | |
15 | #define ST_MIN_IO 1 | |
16 | #define ST_MAX_RELATIVE_THROUGHPUT 100 | |
17 | #define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7 | |
18 | #define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT) | |
19 | #define ST_VERSION "0.2.0" | |
20 | ||
21 | struct selector { | |
22 | struct list_head valid_paths; | |
23 | struct list_head failed_paths; | |
24 | }; | |
25 | ||
26 | struct path_info { | |
27 | struct list_head list; | |
28 | struct dm_path *path; | |
29 | unsigned repeat_count; | |
30 | unsigned relative_throughput; | |
31 | atomic_t in_flight_size; /* Total size of in-flight I/Os */ | |
32 | }; | |
33 | ||
34 | static struct selector *alloc_selector(void) | |
35 | { | |
36 | struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL); | |
37 | ||
38 | if (s) { | |
39 | INIT_LIST_HEAD(&s->valid_paths); | |
40 | INIT_LIST_HEAD(&s->failed_paths); | |
41 | } | |
42 | ||
43 | return s; | |
44 | } | |
45 | ||
46 | static int st_create(struct path_selector *ps, unsigned argc, char **argv) | |
47 | { | |
48 | struct selector *s = alloc_selector(); | |
49 | ||
50 | if (!s) | |
51 | return -ENOMEM; | |
52 | ||
53 | ps->context = s; | |
54 | return 0; | |
55 | } | |
56 | ||
57 | static void free_paths(struct list_head *paths) | |
58 | { | |
59 | struct path_info *pi, *next; | |
60 | ||
61 | list_for_each_entry_safe(pi, next, paths, list) { | |
62 | list_del(&pi->list); | |
63 | kfree(pi); | |
64 | } | |
65 | } | |
66 | ||
67 | static void st_destroy(struct path_selector *ps) | |
68 | { | |
69 | struct selector *s = ps->context; | |
70 | ||
71 | free_paths(&s->valid_paths); | |
72 | free_paths(&s->failed_paths); | |
73 | kfree(s); | |
74 | ps->context = NULL; | |
75 | } | |
76 | ||
77 | static int st_status(struct path_selector *ps, struct dm_path *path, | |
78 | status_type_t type, char *result, unsigned maxlen) | |
79 | { | |
80 | unsigned sz = 0; | |
81 | struct path_info *pi; | |
82 | ||
83 | if (!path) | |
84 | DMEMIT("0 "); | |
85 | else { | |
86 | pi = path->pscontext; | |
87 | ||
88 | switch (type) { | |
89 | case STATUSTYPE_INFO: | |
90 | DMEMIT("%d %u ", atomic_read(&pi->in_flight_size), | |
91 | pi->relative_throughput); | |
92 | break; | |
93 | case STATUSTYPE_TABLE: | |
94 | DMEMIT("%u %u ", pi->repeat_count, | |
95 | pi->relative_throughput); | |
96 | break; | |
97 | } | |
98 | } | |
99 | ||
100 | return sz; | |
101 | } | |
102 | ||
103 | static int st_add_path(struct path_selector *ps, struct dm_path *path, | |
104 | int argc, char **argv, char **error) | |
105 | { | |
106 | struct selector *s = ps->context; | |
107 | struct path_info *pi; | |
108 | unsigned repeat_count = ST_MIN_IO; | |
109 | unsigned relative_throughput = 1; | |
110 | ||
111 | /* | |
112 | * Arguments: [<repeat_count> [<relative_throughput>]] | |
113 | * <repeat_count>: The number of I/Os before switching path. | |
114 | * If not given, default (ST_MIN_IO) is used. | |
115 | * <relative_throughput>: The relative throughput value of | |
116 | * the path among all paths in the path-group. | |
117 | * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT> | |
118 | * If not given, minimum value '1' is used. | |
119 | * If '0' is given, the path isn't selected while | |
120 | * other paths having a positive value are | |
121 | * available. | |
122 | */ | |
123 | if (argc > 2) { | |
124 | *error = "service-time ps: incorrect number of arguments"; | |
125 | return -EINVAL; | |
126 | } | |
127 | ||
128 | if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) { | |
129 | *error = "service-time ps: invalid repeat count"; | |
130 | return -EINVAL; | |
131 | } | |
132 | ||
133 | if ((argc == 2) && | |
134 | (sscanf(argv[1], "%u", &relative_throughput) != 1 || | |
135 | relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) { | |
136 | *error = "service-time ps: invalid relative_throughput value"; | |
137 | return -EINVAL; | |
138 | } | |
139 | ||
140 | /* allocate the path */ | |
141 | pi = kmalloc(sizeof(*pi), GFP_KERNEL); | |
142 | if (!pi) { | |
143 | *error = "service-time ps: Error allocating path context"; | |
144 | return -ENOMEM; | |
145 | } | |
146 | ||
147 | pi->path = path; | |
148 | pi->repeat_count = repeat_count; | |
149 | pi->relative_throughput = relative_throughput; | |
150 | atomic_set(&pi->in_flight_size, 0); | |
151 | ||
152 | path->pscontext = pi; | |
153 | ||
154 | list_add_tail(&pi->list, &s->valid_paths); | |
155 | ||
156 | return 0; | |
157 | } | |
158 | ||
159 | static void st_fail_path(struct path_selector *ps, struct dm_path *path) | |
160 | { | |
161 | struct selector *s = ps->context; | |
162 | struct path_info *pi = path->pscontext; | |
163 | ||
164 | list_move(&pi->list, &s->failed_paths); | |
165 | } | |
166 | ||
167 | static int st_reinstate_path(struct path_selector *ps, struct dm_path *path) | |
168 | { | |
169 | struct selector *s = ps->context; | |
170 | struct path_info *pi = path->pscontext; | |
171 | ||
172 | list_move_tail(&pi->list, &s->valid_paths); | |
173 | ||
174 | return 0; | |
175 | } | |
176 | ||
177 | /* | |
178 | * Compare the estimated service time of 2 paths, pi1 and pi2, | |
179 | * for the incoming I/O. | |
180 | * | |
181 | * Returns: | |
182 | * < 0 : pi1 is better | |
183 | * 0 : no difference between pi1 and pi2 | |
184 | * > 0 : pi2 is better | |
185 | * | |
186 | * Description: | |
187 | * Basically, the service time is estimated by: | |
188 | * ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput' | |
189 | * To reduce the calculation, some optimizations are made. | |
190 | * (See comments inline) | |
191 | */ | |
192 | static int st_compare_load(struct path_info *pi1, struct path_info *pi2, | |
193 | size_t incoming) | |
194 | { | |
195 | size_t sz1, sz2, st1, st2; | |
196 | ||
197 | sz1 = atomic_read(&pi1->in_flight_size); | |
198 | sz2 = atomic_read(&pi2->in_flight_size); | |
199 | ||
200 | /* | |
201 | * Case 1: Both have same throughput value. Choose less loaded path. | |
202 | */ | |
203 | if (pi1->relative_throughput == pi2->relative_throughput) | |
204 | return sz1 - sz2; | |
205 | ||
206 | /* | |
207 | * Case 2a: Both have same load. Choose higher throughput path. | |
208 | * Case 2b: One path has no throughput value. Choose the other one. | |
209 | */ | |
210 | if (sz1 == sz2 || | |
211 | !pi1->relative_throughput || !pi2->relative_throughput) | |
212 | return pi2->relative_throughput - pi1->relative_throughput; | |
213 | ||
214 | /* | |
215 | * Case 3: Calculate service time. Choose faster path. | |
216 | * Service time using pi1: | |
217 | * st1 = (sz1 + incoming) / pi1->relative_throughput | |
218 | * Service time using pi2: | |
219 | * st2 = (sz2 + incoming) / pi2->relative_throughput | |
220 | * | |
221 | * To avoid the division, transform the expression to use | |
222 | * multiplication. | |
223 | * Because ->relative_throughput > 0 here, if st1 < st2, | |
224 | * the expressions below are the same meaning: | |
225 | * (sz1 + incoming) / pi1->relative_throughput < | |
226 | * (sz2 + incoming) / pi2->relative_throughput | |
227 | * (sz1 + incoming) * pi2->relative_throughput < | |
228 | * (sz2 + incoming) * pi1->relative_throughput | |
229 | * So use the later one. | |
230 | */ | |
231 | sz1 += incoming; | |
232 | sz2 += incoming; | |
233 | if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE || | |
234 | sz2 >= ST_MAX_INFLIGHT_SIZE)) { | |
235 | /* | |
236 | * Size may be too big for multiplying pi->relative_throughput | |
237 | * and overflow. | |
238 | * To avoid the overflow and mis-selection, shift down both. | |
239 | */ | |
240 | sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT; | |
241 | sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT; | |
242 | } | |
243 | st1 = sz1 * pi2->relative_throughput; | |
244 | st2 = sz2 * pi1->relative_throughput; | |
245 | if (st1 != st2) | |
246 | return st1 - st2; | |
247 | ||
248 | /* | |
249 | * Case 4: Service time is equal. Choose higher throughput path. | |
250 | */ | |
251 | return pi2->relative_throughput - pi1->relative_throughput; | |
252 | } | |
253 | ||
254 | static struct dm_path *st_select_path(struct path_selector *ps, | |
255 | unsigned *repeat_count, size_t nr_bytes) | |
256 | { | |
257 | struct selector *s = ps->context; | |
258 | struct path_info *pi = NULL, *best = NULL; | |
259 | ||
260 | if (list_empty(&s->valid_paths)) | |
261 | return NULL; | |
262 | ||
263 | /* Change preferred (first in list) path to evenly balance. */ | |
264 | list_move_tail(s->valid_paths.next, &s->valid_paths); | |
265 | ||
266 | list_for_each_entry(pi, &s->valid_paths, list) | |
267 | if (!best || (st_compare_load(pi, best, nr_bytes) < 0)) | |
268 | best = pi; | |
269 | ||
270 | if (!best) | |
271 | return NULL; | |
272 | ||
273 | *repeat_count = best->repeat_count; | |
274 | ||
275 | return best->path; | |
276 | } | |
277 | ||
278 | static int st_start_io(struct path_selector *ps, struct dm_path *path, | |
279 | size_t nr_bytes) | |
280 | { | |
281 | struct path_info *pi = path->pscontext; | |
282 | ||
283 | atomic_add(nr_bytes, &pi->in_flight_size); | |
284 | ||
285 | return 0; | |
286 | } | |
287 | ||
288 | static int st_end_io(struct path_selector *ps, struct dm_path *path, | |
289 | size_t nr_bytes) | |
290 | { | |
291 | struct path_info *pi = path->pscontext; | |
292 | ||
293 | atomic_sub(nr_bytes, &pi->in_flight_size); | |
294 | ||
295 | return 0; | |
296 | } | |
297 | ||
298 | static struct path_selector_type st_ps = { | |
299 | .name = "service-time", | |
300 | .module = THIS_MODULE, | |
301 | .table_args = 2, | |
302 | .info_args = 2, | |
303 | .create = st_create, | |
304 | .destroy = st_destroy, | |
305 | .status = st_status, | |
306 | .add_path = st_add_path, | |
307 | .fail_path = st_fail_path, | |
308 | .reinstate_path = st_reinstate_path, | |
309 | .select_path = st_select_path, | |
310 | .start_io = st_start_io, | |
311 | .end_io = st_end_io, | |
312 | }; | |
313 | ||
314 | static int __init dm_st_init(void) | |
315 | { | |
316 | int r = dm_register_path_selector(&st_ps); | |
317 | ||
318 | if (r < 0) | |
319 | DMERR("register failed %d", r); | |
320 | ||
321 | DMINFO("version " ST_VERSION " loaded"); | |
322 | ||
323 | return r; | |
324 | } | |
325 | ||
326 | static void __exit dm_st_exit(void) | |
327 | { | |
328 | int r = dm_unregister_path_selector(&st_ps); | |
329 | ||
330 | if (r < 0) | |
331 | DMERR("unregister failed %d", r); | |
332 | } | |
333 | ||
334 | module_init(dm_st_init); | |
335 | module_exit(dm_st_exit); | |
336 | ||
337 | MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector"); | |
338 | MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>"); | |
339 | MODULE_LICENSE("GPL"); |