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  *   Benoît 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 /*
 172  * Return whether a BlockBackend has pending requests.
 173  *
 174  * This assumes that tg->lock is held.
 175  *
 176  * @blk: the BlockBackend
 177  * @is_write:  the type of operation (read/write)
 178  * @ret:       whether the BlockBackend has pending requests.
 179  */
 180 static inline bool blk_has_pending_reqs(BlockBackend *blk,
 181                                         bool is_write)
 182 {
 183     const BlockBackendPublic *blkp = blk_get_public(blk);
 184     return blkp->pending_reqs[is_write];
 185 }
 186
 187 /* Return the next BlockBackend in the round-robin sequence with pending I/O
 188  * requests.
 189  *
 190  * This assumes that tg->lock is held.
 191  *
 192  * @blk:       the current BlockBackend
 193  * @is_write:  the type of operation (read/write)
 194  * @ret:       the next BlockBackend with pending requests, or blk if there is
 195  *             none.
 196  */
 197 static BlockBackend *next_throttle_token(BlockBackend *blk, bool is_write)
 198 {
 199     BlockBackendPublic *blkp = blk_get_public(blk);
 200     ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
 201     BlockBackend *token, *start;
 202
 203     start = token = tg->tokens[is_write];
 204
 205     /* get next bs round in round robin style */
 206     token = throttle_group_next_blk(token);
 207     while (token != start && !blk_has_pending_reqs(token, is_write)) {
 208         token = throttle_group_next_blk(token);
 209     }
 210
 211     /* If no IO are queued for scheduling on the next round robin token
 212      * then decide the token is the current bs because chances are
 213      * the current bs get the current request queued.
 214      */
 215     if (token == start && !blk_has_pending_reqs(token, is_write)) {
 216         token = blk;
 217     }
 218
 219     /* Either we return the original BB, or one with pending requests */
 220     assert(token == blk || blk_has_pending_reqs(token, is_write));
 221
 222     return token;
 223 }
 224
 225 /* Check if the next I/O request for a BlockBackend needs to be throttled or
 226  * not. If there's no timer set in this group, set one and update the token
 227  * accordingly.
 228  *
 229  * This assumes that tg->lock is held.
 230  *
 231  * @blk:        the current BlockBackend
 232  * @is_write:   the type of operation (read/write)
 233  * @ret:        whether the I/O request needs to be throttled or not
 234  */
 235 static bool throttle_group_schedule_timer(BlockBackend *blk, bool is_write)
 236 {
 237     BlockBackendPublic *blkp = blk_get_public(blk);
 238     ThrottleState *ts = blkp->throttle_state;
 239     ThrottleTimers *tt = &blkp->throttle_timers;
 240     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 241     bool must_wait;
 242
 243     if (blkp->io_limits_disabled) {
 244         return false;
 245     }
 246
 247     /* Check if any of the timers in this group is already armed */
 248     if (tg->any_timer_armed[is_write]) {
 249         return true;
 250     }
 251
 252     must_wait = throttle_schedule_timer(ts, tt, is_write);
 253
 254     /* If a timer just got armed, set blk as the current token */
 255     if (must_wait) {
 256         tg->tokens[is_write] = blk;
 257         tg->any_timer_armed[is_write] = true;
 258     }
 259
 260     return must_wait;
 261 }
 262
 263 /* Look for the next pending I/O request and schedule it.
 264  *
 265  * This assumes that tg->lock is held.
 266  *
 267  * @blk:       the current BlockBackend
 268  * @is_write:  the type of operation (read/write)
 269  */
 270 static void schedule_next_request(BlockBackend *blk, bool is_write)
 271 {
 272     BlockBackendPublic *blkp = blk_get_public(blk);
 273     ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
 274     bool must_wait;
 275     BlockBackend *token;
 276
 277     /* Check if there's any pending request to schedule next */
 278     token = next_throttle_token(blk, is_write);
 279     if (!blk_has_pending_reqs(token, is_write)) {
 280         return;
 281     }
 282
 283     /* Set a timer for the request if it needs to be throttled */
 284     must_wait = throttle_group_schedule_timer(token, is_write);
 285
 286     /* If it doesn't have to wait, queue it for immediate execution */
 287     if (!must_wait) {
 288         /* Give preference to requests from the current blk */
 289         if (qemu_in_coroutine() &&
 290             qemu_co_queue_next(&blkp->throttled_reqs[is_write])) {
 291             token = blk;
 292         } else {
 293             ThrottleTimers *tt = &blk_get_public(token)->throttle_timers;
 294             int64_t now = qemu_clock_get_ns(tt->clock_type);
 295             timer_mod(tt->timers[is_write], now + 1);
 296             tg->any_timer_armed[is_write] = true;
 297         }
 298         tg->tokens[is_write] = token;
 299     }
 300 }
 301
 302 /* Check if an I/O request needs to be throttled, wait and set a timer
 303  * if necessary, and schedule the next request using a round robin
 304  * algorithm.
 305  *
 306  * @blk:       the current BlockBackend
 307  * @bytes:     the number of bytes for this I/O
 308  * @is_write:  the type of operation (read/write)
 309  */
 310 void coroutine_fn throttle_group_co_io_limits_intercept(BlockBackend *blk,
 311                                                         unsigned int bytes,
 312                                                         bool is_write)
 313 {
 314     bool must_wait;
 315     BlockBackend *token;
 316
 317     BlockBackendPublic *blkp = blk_get_public(blk);
 318     ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
 319     qemu_mutex_lock(&tg->lock);
 320
 321     /* First we check if this I/O has to be throttled. */
 322     token = next_throttle_token(blk, is_write);
 323     must_wait = throttle_group_schedule_timer(token, is_write);
 324
 325     /* Wait if there's a timer set or queued requests of this type */
 326     if (must_wait || blkp->pending_reqs[is_write]) {
 327         blkp->pending_reqs[is_write]++;
 328         qemu_mutex_unlock(&tg->lock);
 329         qemu_co_queue_wait(&blkp->throttled_reqs[is_write]);
 330         qemu_mutex_lock(&tg->lock);
 331         blkp->pending_reqs[is_write]--;
 332     }
 333
 334     /* The I/O will be executed, so do the accounting */
 335     throttle_account(blkp->throttle_state, is_write, bytes);
 336
 337     /* Schedule the next request */
 338     schedule_next_request(blk, is_write);
 339
 340     qemu_mutex_unlock(&tg->lock);
 341 }
 342
 343 void throttle_group_restart_blk(BlockBackend *blk)
 344 {
 345     BlockBackendPublic *blkp = blk_get_public(blk);
 346     int i;
 347
 348     for (i = 0; i < 2; i++) {
 349         while (qemu_co_enter_next(&blkp->throttled_reqs[i])) {
 350             ;
 351         }
 352     }
 353 }
 354
 355 /* Update the throttle configuration for a particular group. Similar
 356  * to throttle_config(), but guarantees atomicity within the
 357  * throttling group.
 358  *
 359  * @blk: a BlockBackend that is a member of the group
 360  * @cfg: the configuration to set
 361  */
 362 void throttle_group_config(BlockBackend *blk, ThrottleConfig *cfg)
 363 {
 364     BlockBackendPublic *blkp = blk_get_public(blk);
 365     ThrottleTimers *tt = &blkp->throttle_timers;
 366     ThrottleState *ts = blkp->throttle_state;
 367     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 368     qemu_mutex_lock(&tg->lock);
 369     /* throttle_config() cancels the timers */
 370     if (timer_pending(tt->timers[0])) {
 371         tg->any_timer_armed[0] = false;
 372     }
 373     if (timer_pending(tt->timers[1])) {
 374         tg->any_timer_armed[1] = false;
 375     }
 376     throttle_config(ts, tt, cfg);
 377     qemu_mutex_unlock(&tg->lock);
 378
 379     qemu_co_enter_next(&blkp->throttled_reqs[0]);
 380     qemu_co_enter_next(&blkp->throttled_reqs[1]);
 381 }
 382
 383 /* Get the throttle configuration from a particular group. Similar to
 384  * throttle_get_config(), but guarantees atomicity within the
 385  * throttling group.
 386  *
 387  * @blk: a BlockBackend that is a member of the group
 388  * @cfg: the configuration will be written here
 389  */
 390 void throttle_group_get_config(BlockBackend *blk, ThrottleConfig *cfg)
 391 {
 392     BlockBackendPublic *blkp = blk_get_public(blk);
 393     ThrottleState *ts = blkp->throttle_state;
 394     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 395     qemu_mutex_lock(&tg->lock);
 396     throttle_get_config(ts, cfg);
 397     qemu_mutex_unlock(&tg->lock);
 398 }
 399
 400 /* ThrottleTimers callback. This wakes up a request that was waiting
 401  * because it had been throttled.
 402  *
 403  * @blk:       the BlockBackend whose request had been throttled
 404  * @is_write:  the type of operation (read/write)
 405  */
 406 static void timer_cb(BlockBackend *blk, bool is_write)
 407 {
 408     BlockBackendPublic *blkp = blk_get_public(blk);
 409     ThrottleState *ts = blkp->throttle_state;
 410     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 411     bool empty_queue;
 412
 413     /* The timer has just been fired, so we can update the flag */
 414     qemu_mutex_lock(&tg->lock);
 415     tg->any_timer_armed[is_write] = false;
 416     qemu_mutex_unlock(&tg->lock);
 417
 418     /* Run the request that was waiting for this timer */
 419     empty_queue = !qemu_co_enter_next(&blkp->throttled_reqs[is_write]);
 420
 421     /* If the request queue was empty then we have to take care of
 422      * scheduling the next one */
 423     if (empty_queue) {
 424         qemu_mutex_lock(&tg->lock);
 425         schedule_next_request(blk, is_write);
 426         qemu_mutex_unlock(&tg->lock);
 427     }
 428 }
 429
 430 static void read_timer_cb(void *opaque)
 431 {
 432     timer_cb(opaque, false);
 433 }
 434
 435 static void write_timer_cb(void *opaque)
 436 {
 437     timer_cb(opaque, true);
 438 }
 439
 440 /* Register a BlockBackend in the throttling group, also initializing its
 441  * timers and updating its throttle_state pointer to point to it. If a
 442  * throttling group with that name does not exist yet, it will be created.
 443  *
 444  * @blk:       the BlockBackend to insert
 445  * @groupname: the name of the group
 446  */
 447 void throttle_group_register_blk(BlockBackend *blk, const char *groupname)
 448 {
 449     int i;
 450     BlockBackendPublic *blkp = blk_get_public(blk);
 451     ThrottleState *ts = throttle_group_incref(groupname);
 452     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 453     int clock_type = QEMU_CLOCK_REALTIME;
 454
 455     if (qtest_enabled()) {
 456         /* For testing block IO throttling only */
 457         clock_type = QEMU_CLOCK_VIRTUAL;
 458     }
 459
 460     blkp->throttle_state = ts;
 461
 462     qemu_mutex_lock(&tg->lock);
 463     /* If the ThrottleGroup is new set this BlockBackend as the token */
 464     for (i = 0; i < 2; i++) {
 465         if (!tg->tokens[i]) {
 466             tg->tokens[i] = blk;
 467         }
 468     }
 469
 470     QLIST_INSERT_HEAD(&tg->head, blkp, round_robin);
 471
 472     throttle_timers_init(&blkp->throttle_timers,
 473                          blk_get_aio_context(blk),
 474                          clock_type,
 475                          read_timer_cb,
 476                          write_timer_cb,
 477                          blk);
 478
 479     qemu_mutex_unlock(&tg->lock);
 480 }
 481
 482 /* Unregister a BlockBackend from its group, removing it from the list,
 483  * destroying the timers and setting the throttle_state pointer to NULL.
 484  *
 485  * The BlockBackend must not have pending throttled requests, so the caller has
 486  * to drain them first.
 487  *
 488  * The group will be destroyed if it's empty after this operation.
 489  *
 490  * @blk: the BlockBackend to remove
 491  */
 492 void throttle_group_unregister_blk(BlockBackend *blk)
 493 {
 494     BlockBackendPublic *blkp = blk_get_public(blk);
 495     ThrottleGroup *tg = container_of(blkp->throttle_state, ThrottleGroup, ts);
 496     int i;
 497
 498     assert(blkp->pending_reqs[0] == 0 && blkp->pending_reqs[1] == 0);
 499     assert(qemu_co_queue_empty(&blkp->throttled_reqs[0]));
 500     assert(qemu_co_queue_empty(&blkp->throttled_reqs[1]));
 501
 502     qemu_mutex_lock(&tg->lock);
 503     for (i = 0; i < 2; i++) {
 504         if (tg->tokens[i] == blk) {
 505             BlockBackend *token = throttle_group_next_blk(blk);
 506             /* Take care of the case where this is the last blk in the group */
 507             if (token == blk) {
 508                 token = NULL;
 509             }
 510             tg->tokens[i] = token;
 511         }
 512     }
 513
 514     /* remove the current blk from the list */
 515     QLIST_REMOVE(blkp, round_robin);
 516     throttle_timers_destroy(&blkp->throttle_timers);
 517     qemu_mutex_unlock(&tg->lock);
 518
 519     throttle_group_unref(&tg->ts);
 520     blkp->throttle_state = NULL;
 521 }
 522
 523 static void throttle_groups_init(void)
 524 {
 525     qemu_mutex_init(&throttle_groups_lock);
 526 }
 527
 528 block_init(throttle_groups_init);