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[sfrench/cifs-2.6.git] / drivers / md / dm-service-time.c
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         /* Change preferred (first in list) path to evenly balance. */
286         list_move_tail(s->valid_paths.next, &s->valid_paths);
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         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)
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");