1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved.
4 *
5 * Module Author: Kiyoshi Ueda
6 *
7 * This file is released under the GPL.
8 *
9 * Throughput oriented path selector.
10 */
11
12#include "dm.h"
13#include "dm-path-selector.h"
14
15#include <linux/slab.h>
16#include <linux/module.h>
17
18#define DM_MSG_PREFIX "multipath service-time"
19#define ST_MIN_IO 1
20#define ST_MAX_RELATIVE_THROUGHPUT 100
21#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7
22#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
23#define ST_VERSION "0.3.0"
24
25struct selector {
26 struct list_head valid_paths;
27 struct list_head failed_paths;
28 spinlock_t lock;
29};
30
31struct path_info {
32 struct list_head list;
33 struct dm_path *path;
34 unsigned int repeat_count;
35 unsigned int relative_throughput;
36 atomic_t in_flight_size; /* Total size of in-flight I/Os */
37};
38
39static struct selector *alloc_selector(void)
40{
41 struct selector *s = kmalloc(size: sizeof(*s), GFP_KERNEL);
42
43 if (s) {
44 INIT_LIST_HEAD(list: &s->valid_paths);
45 INIT_LIST_HEAD(list: &s->failed_paths);
46 spin_lock_init(&s->lock);
47 }
48
49 return s;
50}
51
52static int st_create(struct path_selector *ps, unsigned int argc, char **argv)
53{
54 struct selector *s = alloc_selector();
55
56 if (!s)
57 return -ENOMEM;
58
59 ps->context = s;
60 return 0;
61}
62
63static void free_paths(struct list_head *paths)
64{
65 struct path_info *pi, *next;
66
67 list_for_each_entry_safe(pi, next, paths, list) {
68 list_del(entry: &pi->list);
69 kfree(objp: pi);
70 }
71}
72
73static void st_destroy(struct path_selector *ps)
74{
75 struct selector *s = ps->context;
76
77 free_paths(paths: &s->valid_paths);
78 free_paths(paths: &s->failed_paths);
79 kfree(objp: s);
80 ps->context = NULL;
81}
82
83static int st_status(struct path_selector *ps, struct dm_path *path,
84 status_type_t type, char *result, unsigned int maxlen)
85{
86 unsigned int sz = 0;
87 struct path_info *pi;
88
89 if (!path)
90 DMEMIT("0 ");
91 else {
92 pi = path->pscontext;
93
94 switch (type) {
95 case STATUSTYPE_INFO:
96 DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
97 pi->relative_throughput);
98 break;
99 case STATUSTYPE_TABLE:
100 DMEMIT("%u %u ", pi->repeat_count,
101 pi->relative_throughput);
102 break;
103 case STATUSTYPE_IMA:
104 result[0] = '\0';
105 break;
106 }
107 }
108
109 return sz;
110}
111
112static int st_add_path(struct path_selector *ps, struct dm_path *path,
113 int argc, char **argv, char **error)
114{
115 struct selector *s = ps->context;
116 struct path_info *pi;
117 unsigned int repeat_count = ST_MIN_IO;
118 unsigned int relative_throughput = 1;
119 char dummy;
120 unsigned long flags;
121
122 /*
123 * Arguments: [<repeat_count> [<relative_throughput>]]
124 * <repeat_count>: The number of I/Os before switching path.
125 * If not given, default (ST_MIN_IO) is used.
126 * <relative_throughput>: The relative throughput value of
127 * the path among all paths in the path-group.
128 * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
129 * If not given, minimum value '1' is used.
130 * If '0' is given, the path isn't selected while
131 * other paths having a positive value are 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(size: 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(v: &pi->in_flight_size, i: 0);
166
167 path->pscontext = pi;
168
169 spin_lock_irqsave(&s->lock, flags);
170 list_add_tail(new: &pi->list, head: &s->valid_paths);
171 spin_unlock_irqrestore(lock: &s->lock, flags);
172
173 return 0;
174}
175
176static 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(list: &pi->list, head: &s->failed_paths);
184 spin_unlock_irqrestore(lock: &s->lock, flags);
185}
186
187static 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(list: &pi->list, head: &s->valid_paths);
195 spin_unlock_irqrestore(lock: &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 */
215static 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(v: &pi1->in_flight_size);
221 sz2 = atomic_read(v: &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
277static 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(head: &s->valid_paths))
286 goto out;
287
288 list_for_each_entry(pi, &s->valid_paths, list)
289 if (!best || (st_compare_load(pi1: pi, pi2: best, incoming: 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(list: &best->list, head: &s->valid_paths);
297
298 ret = best->path;
299out:
300 spin_unlock_irqrestore(lock: &s->lock, flags);
301 return ret;
302}
303
304static 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(i: nr_bytes, v: &pi->in_flight_size);
310
311 return 0;
312}
313
314static 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(i: nr_bytes, v: &pi->in_flight_size);
320
321 return 0;
322}
323
324static 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
340static int __init dm_st_init(void)
341{
342 int r = dm_register_path_selector(type: &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
352static void __exit dm_st_exit(void)
353{
354 int r = dm_unregister_path_selector(type: &st_ps);
355
356 if (r < 0)
357 DMERR("unregister failed %d", r);
358}
359
360module_init(dm_st_init);
361module_exit(dm_st_exit);
362
363MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
364MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
365MODULE_LICENSE("GPL");
366

source code of linux/drivers/md/dm-ps-service-time.c