linux-user: Use safe_syscall for open and openat system calls
[qemu.git] / block / throttle-groups.c
1 /*
2 * QEMU block throttling group infrastructure
3 *
4 * Copyright (C) Nodalink, EURL. 2014
5 * Copyright (C) Igalia, S.L. 2015
6 *
7 * Authors:
8 * BenoƮt Canet <benoit.canet@nodalink.com>
9 * Alberto Garcia <berto@igalia.com>
10 *
11 * This program is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU General Public License as
13 * published by the Free Software Foundation; either version 2 or
14 * (at your option) version 3 of the License.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, see <http://www.gnu.org/licenses/>.
23 */
24
25 #include "qemu/osdep.h"
26 #include "sysemu/block-backend.h"
27 #include "block/throttle-groups.h"
28 #include "qemu/queue.h"
29 #include "qemu/thread.h"
30 #include "sysemu/qtest.h"
31
32 /* The ThrottleGroup structure (with its ThrottleState) is shared
33 * among different BlockBackends and it's independent from
34 * AioContext, so in order to use it from different threads it needs
35 * its own locking.
36 *
37 * This locking is however handled internally in this file, so it's
38 * transparent to outside users.
39 *
40 * The whole ThrottleGroup structure is private and invisible to
41 * outside users, that only use it through its ThrottleState.
42 *
43 * In addition to the ThrottleGroup structure, BlockBackendPublic has
44 * fields that need to be accessed by other members of the group and
45 * therefore also need to be protected by this lock. Once a
46 * BlockBackend is registered in a group those fields can be accessed
47 * by other threads any time.
48 *
49 * Again, all this is handled internally and is mostly transparent to
50 * the outside. The 'throttle_timers' field however has an additional
51 * constraint because it may be temporarily invalid (see for example
52 * bdrv_set_aio_context()). Therefore in this file a thread will
53 * access some other BlockBackend's timers only after verifying that
54 * that BlockBackend has throttled requests in the queue.
55 */
56 typedef struct ThrottleGroup {
57 char *name; /* This is constant during the lifetime of the group */
58
59 QemuMutex lock; /* This lock protects the following four fields */
60 ThrottleState ts;
61 QLIST_HEAD(, BlockBackendPublic) head;
62 BlockBackend *tokens[2];
63 bool any_timer_armed[2];
64
65 /* These two are protected by the global throttle_groups_lock */
66 unsigned refcount;
67 QTAILQ_ENTRY(ThrottleGroup) list;
68 } ThrottleGroup;
69
70 static QemuMutex throttle_groups_lock;
71 static QTAILQ_HEAD(, ThrottleGroup) throttle_groups =
72 QTAILQ_HEAD_INITIALIZER(throttle_groups);
73
74 /* Increments the reference count of a ThrottleGroup given its name.
75 *
76 * If no ThrottleGroup is found with the given name a new one is
77 * created.
78 *
79 * @name: the name of the ThrottleGroup
80 * @ret: the ThrottleState member of the ThrottleGroup
81 */
82 ThrottleState *throttle_group_incref(const char *name)
83 {
84 ThrottleGroup *tg = NULL;
85 ThrottleGroup *iter;
86
87 qemu_mutex_lock(&throttle_groups_lock);
88
89 /* Look for an existing group with that name */
90 QTAILQ_FOREACH(iter, &throttle_groups, list) {
91 if (!strcmp(name, iter->name)) {
92 tg = iter;
93 break;
94 }
95 }
96
97 /* Create a new one if not found */
98 if (!tg) {
99 tg = g_new0(ThrottleGroup, 1);
100 tg->name = g_strdup(name);
101 qemu_mutex_init(&tg->lock);
102 throttle_init(&tg->ts);
103 QLIST_INIT(&tg->head);
104
105 QTAILQ_INSERT_TAIL(&throttle_groups, tg, list);
106 }
107
108 tg->refcount++;
109
110 qemu_mutex_unlock(&throttle_groups_lock);
111
112 return &tg->ts;
113 }
114
115 /* Decrease the reference count of a ThrottleGroup.
116 *
117 * When the reference count reaches zero the ThrottleGroup is
118 * destroyed.
119 *
120 * @ts: The ThrottleGroup to unref, given by its ThrottleState member
121 */
122 void throttle_group_unref(ThrottleState *ts)
123 {
124 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
125
126 qemu_mutex_lock(&throttle_groups_lock);
127 if (--tg->refcount == 0) {
128 QTAILQ_REMOVE(&throttle_groups, tg, list);
129 qemu_mutex_destroy(&tg->lock);
130 g_free(tg->name);
131 g_free(tg);
132 }
133 qemu_mutex_unlock(&throttle_groups_lock);
134 }
135
136 /* Get the name from a BlockBackend's ThrottleGroup. The name (and the pointer)
137 * is guaranteed to remain constant during the lifetime of the group.
138 *
139 * @blk: a BlockBackend that is member of a throttling group
140 * @ret: the name of the group.
141 */
142 const char *throttle_group_get_name(BlockBackend *blk)
143 {
144 BlockBackendPublic *blkp = blk_get_public(blk);
145 ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
146 return tg->name;
147 }
148
149 /* Return the next BlockBackend in the round-robin sequence, simulating a
150 * circular list.
151 *
152 * This assumes that tg->lock is held.
153 *
154 * @blk: the current BlockBackend
155 * @ret: the next BlockBackend in the sequence
156 */
157 static BlockBackend *throttle_group_next_blk(BlockBackend *blk)
158 {
159 BlockBackendPublic *blkp = blk_get_public(blk);
160 ThrottleState *ts = blkp->throttle_state;
161 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
162 BlockBackendPublic *next = QLIST_NEXT(blkp, round_robin);
163
164 if (!next) {
165 next = QLIST_FIRST(&tg->head);
166 }
167
168 return blk_by_public(next);
169 }
170
171 /* Return the next BlockBackend in the round-robin sequence with pending I/O
172 * requests.
173 *
174 * This assumes that tg->lock is held.
175 *
176 * @blk: the current BlockBackend
177 * @is_write: the type of operation (read/write)
178 * @ret: the next BlockBackend with pending requests, or blk if there is
179 * none.
180 */
181 static BlockBackend *next_throttle_token(BlockBackend *blk, bool is_write)
182 {
183 BlockBackendPublic *blkp = blk_get_public(blk);
184 ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
185 BlockBackend *token, *start;
186
187 start = token = tg->tokens[is_write];
188
189 /* get next bs round in round robin style */
190 token = throttle_group_next_blk(token);
191 while (token != start && !blkp->pending_reqs[is_write]) {
192 token = throttle_group_next_blk(token);
193 }
194
195 /* If no IO are queued for scheduling on the next round robin token
196 * then decide the token is the current bs because chances are
197 * the current bs get the current request queued.
198 */
199 if (token == start && !blkp->pending_reqs[is_write]) {
200 token = blk;
201 }
202
203 return token;
204 }
205
206 /* Check if the next I/O request for a BlockBackend needs to be throttled or
207 * not. If there's no timer set in this group, set one and update the token
208 * accordingly.
209 *
210 * This assumes that tg->lock is held.
211 *
212 * @blk: the current BlockBackend
213 * @is_write: the type of operation (read/write)
214 * @ret: whether the I/O request needs to be throttled or not
215 */
216 static bool throttle_group_schedule_timer(BlockBackend *blk, bool is_write)
217 {
218 BlockBackendPublic *blkp = blk_get_public(blk);
219 ThrottleState *ts = blkp->throttle_state;
220 ThrottleTimers *tt = &blkp->throttle_timers;
221 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
222 bool must_wait;
223
224 if (blkp->io_limits_disabled) {
225 return false;
226 }
227
228 /* Check if any of the timers in this group is already armed */
229 if (tg->any_timer_armed[is_write]) {
230 return true;
231 }
232
233 must_wait = throttle_schedule_timer(ts, tt, is_write);
234
235 /* If a timer just got armed, set blk as the current token */
236 if (must_wait) {
237 tg->tokens[is_write] = blk;
238 tg->any_timer_armed[is_write] = true;
239 }
240
241 return must_wait;
242 }
243
244 /* Look for the next pending I/O request and schedule it.
245 *
246 * This assumes that tg->lock is held.
247 *
248 * @blk: the current BlockBackend
249 * @is_write: the type of operation (read/write)
250 */
251 static void schedule_next_request(BlockBackend *blk, bool is_write)
252 {
253 BlockBackendPublic *blkp = blk_get_public(blk);
254 ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
255 bool must_wait;
256 BlockBackend *token;
257
258 /* Check if there's any pending request to schedule next */
259 token = next_throttle_token(blk, is_write);
260 if (!blkp->pending_reqs[is_write]) {
261 return;
262 }
263
264 /* Set a timer for the request if it needs to be throttled */
265 must_wait = throttle_group_schedule_timer(token, is_write);
266
267 /* If it doesn't have to wait, queue it for immediate execution */
268 if (!must_wait) {
269 /* Give preference to requests from the current blk */
270 if (qemu_in_coroutine() &&
271 qemu_co_queue_next(&blkp->throttled_reqs[is_write])) {
272 token = blk;
273 } else {
274 ThrottleTimers *tt = &blkp->throttle_timers;
275 int64_t now = qemu_clock_get_ns(tt->clock_type);
276 timer_mod(tt->timers[is_write], now + 1);
277 tg->any_timer_armed[is_write] = true;
278 }
279 tg->tokens[is_write] = token;
280 }
281 }
282
283 /* Check if an I/O request needs to be throttled, wait and set a timer
284 * if necessary, and schedule the next request using a round robin
285 * algorithm.
286 *
287 * @blk: the current BlockBackend
288 * @bytes: the number of bytes for this I/O
289 * @is_write: the type of operation (read/write)
290 */
291 void coroutine_fn throttle_group_co_io_limits_intercept(BlockBackend *blk,
292 unsigned int bytes,
293 bool is_write)
294 {
295 bool must_wait;
296 BlockBackend *token;
297
298 BlockBackendPublic *blkp = blk_get_public(blk);
299 ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
300 qemu_mutex_lock(&tg->lock);
301
302 /* First we check if this I/O has to be throttled. */
303 token = next_throttle_token(blk, is_write);
304 must_wait = throttle_group_schedule_timer(token, is_write);
305
306 /* Wait if there's a timer set or queued requests of this type */
307 if (must_wait || blkp->pending_reqs[is_write]) {
308 blkp->pending_reqs[is_write]++;
309 qemu_mutex_unlock(&tg->lock);
310 qemu_co_queue_wait(&blkp->throttled_reqs[is_write]);
311 qemu_mutex_lock(&tg->lock);
312 blkp->pending_reqs[is_write]--;
313 }
314
315 /* The I/O will be executed, so do the accounting */
316 throttle_account(blkp->throttle_state, is_write, bytes);
317
318 /* Schedule the next request */
319 schedule_next_request(blk, is_write);
320
321 qemu_mutex_unlock(&tg->lock);
322 }
323
324 void throttle_group_restart_blk(BlockBackend *blk)
325 {
326 BlockBackendPublic *blkp = blk_get_public(blk);
327 int i;
328
329 for (i = 0; i < 2; i++) {
330 while (qemu_co_enter_next(&blkp->throttled_reqs[i])) {
331 ;
332 }
333 }
334 }
335
336 /* Update the throttle configuration for a particular group. Similar
337 * to throttle_config(), but guarantees atomicity within the
338 * throttling group.
339 *
340 * @blk: a BlockBackend that is a member of the group
341 * @cfg: the configuration to set
342 */
343 void throttle_group_config(BlockBackend *blk, ThrottleConfig *cfg)
344 {
345 BlockBackendPublic *blkp = blk_get_public(blk);
346 ThrottleTimers *tt = &blkp->throttle_timers;
347 ThrottleState *ts = blkp->throttle_state;
348 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
349 qemu_mutex_lock(&tg->lock);
350 /* throttle_config() cancels the timers */
351 if (timer_pending(tt->timers[0])) {
352 tg->any_timer_armed[0] = false;
353 }
354 if (timer_pending(tt->timers[1])) {
355 tg->any_timer_armed[1] = false;
356 }
357 throttle_config(ts, tt, cfg);
358 qemu_mutex_unlock(&tg->lock);
359
360 qemu_co_enter_next(&blkp->throttled_reqs[0]);
361 qemu_co_enter_next(&blkp->throttled_reqs[1]);
362 }
363
364 /* Get the throttle configuration from a particular group. Similar to
365 * throttle_get_config(), but guarantees atomicity within the
366 * throttling group.
367 *
368 * @blk: a BlockBackend that is a member of the group
369 * @cfg: the configuration will be written here
370 */
371 void throttle_group_get_config(BlockBackend *blk, ThrottleConfig *cfg)
372 {
373 BlockBackendPublic *blkp = blk_get_public(blk);
374 ThrottleState *ts = blkp->throttle_state;
375 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
376 qemu_mutex_lock(&tg->lock);
377 throttle_get_config(ts, cfg);
378 qemu_mutex_unlock(&tg->lock);
379 }
380
381 /* ThrottleTimers callback. This wakes up a request that was waiting
382 * because it had been throttled.
383 *
384 * @blk: the BlockBackend whose request had been throttled
385 * @is_write: the type of operation (read/write)
386 */
387 static void timer_cb(BlockBackend *blk, bool is_write)
388 {
389 BlockBackendPublic *blkp = blk_get_public(blk);
390 ThrottleState *ts = blkp->throttle_state;
391 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
392 bool empty_queue;
393
394 /* The timer has just been fired, so we can update the flag */
395 qemu_mutex_lock(&tg->lock);
396 tg->any_timer_armed[is_write] = false;
397 qemu_mutex_unlock(&tg->lock);
398
399 /* Run the request that was waiting for this timer */
400 empty_queue = !qemu_co_enter_next(&blkp->throttled_reqs[is_write]);
401
402 /* If the request queue was empty then we have to take care of
403 * scheduling the next one */
404 if (empty_queue) {
405 qemu_mutex_lock(&tg->lock);
406 schedule_next_request(blk, is_write);
407 qemu_mutex_unlock(&tg->lock);
408 }
409 }
410
411 static void read_timer_cb(void *opaque)
412 {
413 timer_cb(opaque, false);
414 }
415
416 static void write_timer_cb(void *opaque)
417 {
418 timer_cb(opaque, true);
419 }
420
421 /* Register a BlockBackend in the throttling group, also initializing its
422 * timers and updating its throttle_state pointer to point to it. If a
423 * throttling group with that name does not exist yet, it will be created.
424 *
425 * @blk: the BlockBackend to insert
426 * @groupname: the name of the group
427 */
428 void throttle_group_register_blk(BlockBackend *blk, const char *groupname)
429 {
430 int i;
431 BlockBackendPublic *blkp = blk_get_public(blk);
432 ThrottleState *ts = throttle_group_incref(groupname);
433 ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
434 int clock_type = QEMU_CLOCK_REALTIME;
435
436 if (qtest_enabled()) {
437 /* For testing block IO throttling only */
438 clock_type = QEMU_CLOCK_VIRTUAL;
439 }
440
441 blkp->throttle_state = ts;
442
443 qemu_mutex_lock(&tg->lock);
444 /* If the ThrottleGroup is new set this BlockBackend as the token */
445 for (i = 0; i < 2; i++) {
446 if (!tg->tokens[i]) {
447 tg->tokens[i] = blk;
448 }
449 }
450
451 QLIST_INSERT_HEAD(&tg->head, blkp, round_robin);
452
453 throttle_timers_init(&blkp->throttle_timers,
454 blk_get_aio_context(blk),
455 clock_type,
456 read_timer_cb,
457 write_timer_cb,
458 blk);
459
460 qemu_mutex_unlock(&tg->lock);
461 }
462
463 /* Unregister a BlockBackend from its group, removing it from the list,
464 * destroying the timers and setting the throttle_state pointer to NULL.
465 *
466 * The BlockBackend must not have pending throttled requests, so the caller has
467 * to drain them first.
468 *
469 * The group will be destroyed if it's empty after this operation.
470 *
471 * @blk: the BlockBackend to remove
472 */
473 void throttle_group_unregister_blk(BlockBackend *blk)
474 {
475 BlockBackendPublic *blkp = blk_get_public(blk);
476 ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
477 int i;
478
479 assert(blkp->pending_reqs[0] == 0 && blkp->pending_reqs[1] == 0);
480 assert(qemu_co_queue_empty(&blkp->throttled_reqs[0]));
481 assert(qemu_co_queue_empty(&blkp->throttled_reqs[1]));
482
483 qemu_mutex_lock(&tg->lock);
484 for (i = 0; i < 2; i++) {
485 if (tg->tokens[i] == blk) {
486 BlockBackend *token = throttle_group_next_blk(blk);
487 /* Take care of the case where this is the last blk in the group */
488 if (token == blk) {
489 token = NULL;
490 }
491 tg->tokens[i] = token;
492 }
493 }
494
495 /* remove the current blk from the list */
496 QLIST_REMOVE(blkp, round_robin);
497 throttle_timers_destroy(&blkp->throttle_timers);
498 qemu_mutex_unlock(&tg->lock);
499
500 throttle_group_unref(&tg->ts);
501 blkp->throttle_state = NULL;
502 }
503
504 static void throttle_groups_init(void)
505 {
506 qemu_mutex_init(&throttle_groups_lock);
507 }
508
509 block_init(throttle_groups_init);