util/throttle.c

   1 /*
   2  * QEMU throttling infrastructure
   3  *
   4  * Copyright (C) Nodalink, EURL. 2013-2014
   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 "qapi/error.h"
  27 #include "qemu/throttle.h"
  28 #include "qemu/timer.h"
  29 #include "block/aio.h"
  30
  31 /* This function make a bucket leak
  32  *
  33  * @bkt:   the bucket to make leak
  34  * @delta_ns: the time delta
  35  */
  36 void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta_ns)
  37 {
  38     double leak;
  39
  40     /* compute how much to leak */
  41     leak = (bkt->avg * (double) delta_ns) / NANOSECONDS_PER_SECOND;
  42
  43     /* make the bucket leak */
  44     bkt->level = MAX(bkt->level - leak, 0);
  45
  46     /* if we allow bursts for more than one second we also need to
  47      * keep track of bkt->burst_level so the bkt->max goal per second
  48      * is attained */
  49     if (bkt->burst_length > 1) {
  50         leak = (bkt->max * (double) delta_ns) / NANOSECONDS_PER_SECOND;
  51         bkt->burst_level = MAX(bkt->burst_level - leak, 0);
  52     }
  53 }
  54
  55 /* Calculate the time delta since last leak and make proportionals leaks
  56  *
  57  * @now:      the current timestamp in ns
  58  */
  59 static void throttle_do_leak(ThrottleState *ts, int64_t now)
  60 {
  61     /* compute the time elapsed since the last leak */
  62     int64_t delta_ns = now - ts->previous_leak;
  63     int i;
  64
  65     ts->previous_leak = now;
  66
  67     if (delta_ns <= 0) {
  68         return;
  69     }
  70
  71     /* make each bucket leak */
  72     for (i = 0; i < BUCKETS_COUNT; i++) {
  73         throttle_leak_bucket(&ts->cfg.buckets[i], delta_ns);
  74     }
  75 }
  76
  77 /* do the real job of computing the time to wait
  78  *
  79  * @limit: the throttling limit
  80  * @extra: the number of operation to delay
  81  * @ret:   the time to wait in ns
  82  */
  83 static int64_t throttle_do_compute_wait(double limit, double extra)
  84 {
  85     double wait = extra * NANOSECONDS_PER_SECOND;
  86     wait /= limit;
  87     return wait;
  88 }
  89
  90 /* This function compute the wait time in ns that a leaky bucket should trigger
  91  *
  92  * @bkt: the leaky bucket we operate on
  93  * @ret: the resulting wait time in ns or 0 if the operation can go through
  94  */
  95 int64_t throttle_compute_wait(LeakyBucket *bkt)
  96 {
  97     double extra; /* the number of extra units blocking the io */
  98
  99     if (!bkt->avg) {
 100         return 0;
 101     }
 102
 103     /* If the bucket is full then we have to wait */
 104     extra = bkt->level - bkt->max * bkt->burst_length;
 105     if (extra > 0) {
 106         return throttle_do_compute_wait(bkt->avg, extra);
 107     }
 108
 109     /* If the bucket is not full yet we have to make sure that we
 110      * fulfill the goal of bkt->max units per second. */
 111     if (bkt->burst_length > 1) {
 112         /* We use 1/10 of the max value to smooth the throttling.
 113          * See throttle_fix_bucket() for more details. */
 114         extra = bkt->burst_level - bkt->max / 10;
 115         if (extra > 0) {
 116             return throttle_do_compute_wait(bkt->max, extra);
 117         }
 118     }
 119
 120     return 0;
 121 }
 122
 123 /* This function compute the time that must be waited while this IO
 124  *
 125  * @is_write:   true if the current IO is a write, false if it's a read
 126  * @ret:        time to wait
 127  */
 128 static int64_t throttle_compute_wait_for(ThrottleState *ts,
 129                                          bool is_write)
 130 {
 131     BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
 132                                    THROTTLE_OPS_TOTAL,
 133                                    THROTTLE_BPS_READ,
 134                                    THROTTLE_OPS_READ},
 135                                   {THROTTLE_BPS_TOTAL,
 136                                    THROTTLE_OPS_TOTAL,
 137                                    THROTTLE_BPS_WRITE,
 138                                    THROTTLE_OPS_WRITE}, };
 139     int64_t wait, max_wait = 0;
 140     int i;
 141
 142     for (i = 0; i < 4; i++) {
 143         BucketType index = to_check[is_write][i];
 144         wait = throttle_compute_wait(&ts->cfg.buckets[index]);
 145         if (wait > max_wait) {
 146             max_wait = wait;
 147         }
 148     }
 149
 150     return max_wait;
 151 }
 152
 153 /* compute the timer for this type of operation
 154  *
 155  * @is_write:   the type of operation
 156  * @now:        the current clock timestamp
 157  * @next_timestamp: the resulting timer
 158  * @ret:        true if a timer must be set
 159  */
 160 static bool throttle_compute_timer(ThrottleState *ts,
 161                                    bool is_write,
 162                                    int64_t now,
 163                                    int64_t *next_timestamp)
 164 {
 165     int64_t wait;
 166
 167     /* leak proportionally to the time elapsed */
 168     throttle_do_leak(ts, now);
 169
 170     /* compute the wait time if any */
 171     wait = throttle_compute_wait_for(ts, is_write);
 172
 173     /* if the code must wait compute when the next timer should fire */
 174     if (wait) {
 175         *next_timestamp = now + wait;
 176         return true;
 177     }
 178
 179     /* else no need to wait at all */
 180     *next_timestamp = now;
 181     return false;
 182 }
 183
 184 /* Add timers to event loop */
 185 void throttle_timers_attach_aio_context(ThrottleTimers *tt,
 186                                         AioContext *new_context)
 187 {
 188     tt->timers[0] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
 189                                   tt->read_timer_cb, tt->timer_opaque);
 190     tt->timers[1] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
 191                                   tt->write_timer_cb, tt->timer_opaque);
 192 }
 193
 194 /*
 195  * Initialize the ThrottleConfig structure to a valid state
 196  * @cfg: the config to initialize
 197  */
 198 void throttle_config_init(ThrottleConfig *cfg)
 199 {
 200     unsigned i;
 201     memset(cfg, 0, sizeof(*cfg));
 202     for (i = 0; i < BUCKETS_COUNT; i++) {
 203         cfg->buckets[i].burst_length = 1;
 204     }
 205 }
 206
 207 /* To be called first on the ThrottleState */
 208 void throttle_init(ThrottleState *ts)
 209 {
 210     memset(ts, 0, sizeof(ThrottleState));
 211     throttle_config_init(&ts->cfg);
 212 }
 213
 214 /* To be called first on the ThrottleTimers */
 215 void throttle_timers_init(ThrottleTimers *tt,
 216                           AioContext *aio_context,
 217                           QEMUClockType clock_type,
 218                           QEMUTimerCB *read_timer_cb,
 219                           QEMUTimerCB *write_timer_cb,
 220                           void *timer_opaque)
 221 {
 222     memset(tt, 0, sizeof(ThrottleTimers));
 223
 224     tt->clock_type = clock_type;
 225     tt->read_timer_cb = read_timer_cb;
 226     tt->write_timer_cb = write_timer_cb;
 227     tt->timer_opaque = timer_opaque;
 228     throttle_timers_attach_aio_context(tt, aio_context);
 229 }
 230
 231 /* destroy a timer */
 232 static void throttle_timer_destroy(QEMUTimer **timer)
 233 {
 234     assert(*timer != NULL);
 235
 236     timer_del(*timer);
 237     timer_free(*timer);
 238     *timer = NULL;
 239 }
 240
 241 /* Remove timers from event loop */
 242 void throttle_timers_detach_aio_context(ThrottleTimers *tt)
 243 {
 244     int i;
 245
 246     for (i = 0; i < 2; i++) {
 247         throttle_timer_destroy(&tt->timers[i]);
 248     }
 249 }
 250
 251 /* To be called last on the ThrottleTimers */
 252 void throttle_timers_destroy(ThrottleTimers *tt)
 253 {
 254     throttle_timers_detach_aio_context(tt);
 255 }
 256
 257 /* is any throttling timer configured */
 258 bool throttle_timers_are_initialized(ThrottleTimers *tt)
 259 {
 260     if (tt->timers[0]) {
 261         return true;
 262     }
 263
 264     return false;
 265 }
 266
 267 /* Does any throttling must be done
 268  *
 269  * @cfg: the throttling configuration to inspect
 270  * @ret: true if throttling must be done else false
 271  */
 272 bool throttle_enabled(ThrottleConfig *cfg)
 273 {
 274     int i;
 275
 276     for (i = 0; i < BUCKETS_COUNT; i++) {
 277         if (cfg->buckets[i].avg > 0) {
 278             return true;
 279         }
 280     }
 281
 282     return false;
 283 }
 284
 285 /* check if a throttling configuration is valid
 286  * @cfg: the throttling configuration to inspect
 287  * @ret: true if valid else false
 288  * @errp: error object
 289  */
 290 bool throttle_is_valid(ThrottleConfig *cfg, Error **errp)
 291 {
 292     int i;
 293     bool bps_flag, ops_flag;
 294     bool bps_max_flag, ops_max_flag;
 295
 296     bps_flag = cfg->buckets[THROTTLE_BPS_TOTAL].avg &&
 297                (cfg->buckets[THROTTLE_BPS_READ].avg ||
 298                 cfg->buckets[THROTTLE_BPS_WRITE].avg);
 299
 300     ops_flag = cfg->buckets[THROTTLE_OPS_TOTAL].avg &&
 301                (cfg->buckets[THROTTLE_OPS_READ].avg ||
 302                 cfg->buckets[THROTTLE_OPS_WRITE].avg);
 303
 304     bps_max_flag = cfg->buckets[THROTTLE_BPS_TOTAL].max &&
 305                   (cfg->buckets[THROTTLE_BPS_READ].max  ||
 306                    cfg->buckets[THROTTLE_BPS_WRITE].max);
 307
 308     ops_max_flag = cfg->buckets[THROTTLE_OPS_TOTAL].max &&
 309                    (cfg->buckets[THROTTLE_OPS_READ].max ||
 310                    cfg->buckets[THROTTLE_OPS_WRITE].max);
 311
 312     if (bps_flag || ops_flag || bps_max_flag || ops_max_flag) {
 313         error_setg(errp, "bps/iops/max total values and read/write values"
 314                    " cannot be used at the same time");
 315         return false;
 316     }
 317
 318     for (i = 0; i < BUCKETS_COUNT; i++) {
 319         if (cfg->buckets[i].avg < 0 ||
 320             cfg->buckets[i].max < 0 ||
 321             cfg->buckets[i].avg > THROTTLE_VALUE_MAX ||
 322             cfg->buckets[i].max > THROTTLE_VALUE_MAX) {
 323             error_setg(errp, "bps/iops/max values must be within [0, %lld]",
 324                        THROTTLE_VALUE_MAX);
 325             return false;
 326         }
 327
 328         if (!cfg->buckets[i].burst_length) {
 329             error_setg(errp, "the burst length cannot be 0");
 330             return false;
 331         }
 332
 333         if (cfg->buckets[i].burst_length > 1 && !cfg->buckets[i].max) {
 334             error_setg(errp, "burst length set without burst rate");
 335             return false;
 336         }
 337
 338         if (cfg->buckets[i].max && !cfg->buckets[i].avg) {
 339             error_setg(errp, "bps_max/iops_max require corresponding"
 340                        " bps/iops values");
 341             return false;
 342         }
 343     }
 344
 345     return true;
 346 }
 347
 348 /* fix bucket parameters */
 349 static void throttle_fix_bucket(LeakyBucket *bkt)
 350 {
 351     double min;
 352
 353     /* zero bucket level */
 354     bkt->level = bkt->burst_level = 0;
 355
 356     /* The following is done to cope with the Linux CFQ block scheduler
 357      * which regroup reads and writes by block of 100ms in the guest.
 358      * When they are two process one making reads and one making writes cfq
 359      * make a pattern looking like the following:
 360      * WWWWWWWWWWWRRRRRRRRRRRRRRWWWWWWWWWWWWWwRRRRRRRRRRRRRRRRR
 361      * Having a max burst value of 100ms of the average will help smooth the
 362      * throttling
 363      */
 364     min = bkt->avg / 10;
 365     if (bkt->avg && !bkt->max) {
 366         bkt->max = min;
 367     }
 368 }
 369
 370 /* take care of canceling a timer */
 371 static void throttle_cancel_timer(QEMUTimer *timer)
 372 {
 373     assert(timer != NULL);
 374
 375     timer_del(timer);
 376 }
 377
 378 /* Used to configure the throttle
 379  *
 380  * @ts: the throttle state we are working on
 381  * @tt: the throttle timers we use in this aio context
 382  * @cfg: the config to set
 383  */
 384 void throttle_config(ThrottleState *ts,
 385                      ThrottleTimers *tt,
 386                      ThrottleConfig *cfg)
 387 {
 388     int i;
 389
 390     ts->cfg = *cfg;
 391
 392     for (i = 0; i < BUCKETS_COUNT; i++) {
 393         throttle_fix_bucket(&ts->cfg.buckets[i]);
 394     }
 395
 396     ts->previous_leak = qemu_clock_get_ns(tt->clock_type);
 397
 398     for (i = 0; i < 2; i++) {
 399         throttle_cancel_timer(tt->timers[i]);
 400     }
 401 }
 402
 403 /* used to get config
 404  *
 405  * @ts:  the throttle state we are working on
 406  * @cfg: the config to write
 407  */
 408 void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
 409 {
 410     *cfg = ts->cfg;
 411 }
 412
 413
 414 /* Schedule the read or write timer if needed
 415  *
 416  * NOTE: this function is not unit tested due to it's usage of timer_mod
 417  *
 418  * @tt:       the timers structure
 419  * @is_write: the type of operation (read/write)
 420  * @ret:      true if the timer has been scheduled else false
 421  */
 422 bool throttle_schedule_timer(ThrottleState *ts,
 423                              ThrottleTimers *tt,
 424                              bool is_write)
 425 {
 426     int64_t now = qemu_clock_get_ns(tt->clock_type);
 427     int64_t next_timestamp;
 428     bool must_wait;
 429
 430     must_wait = throttle_compute_timer(ts,
 431                                        is_write,
 432                                        now,
 433                                        &next_timestamp);
 434
 435     /* request not throttled */
 436     if (!must_wait) {
 437         return false;
 438     }
 439
 440     /* request throttled and timer pending -> do nothing */
 441     if (timer_pending(tt->timers[is_write])) {
 442         return true;
 443     }
 444
 445     /* request throttled and timer not pending -> arm timer */
 446     timer_mod(tt->timers[is_write], next_timestamp);
 447     return true;
 448 }
 449
 450 /* do the accounting for this operation
 451  *
 452  * @is_write: the type of operation (read/write)
 453  * @size:     the size of the operation
 454  */
 455 void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
 456 {
 457     const BucketType bucket_types_size[2][2] = {
 458         { THROTTLE_BPS_TOTAL, THROTTLE_BPS_READ },
 459         { THROTTLE_BPS_TOTAL, THROTTLE_BPS_WRITE }
 460     };
 461     const BucketType bucket_types_units[2][2] = {
 462         { THROTTLE_OPS_TOTAL, THROTTLE_OPS_READ },
 463         { THROTTLE_OPS_TOTAL, THROTTLE_OPS_WRITE }
 464     };
 465     double units = 1.0;
 466     unsigned i;
 467
 468     /* if cfg.op_size is defined and smaller than size we compute unit count */
 469     if (ts->cfg.op_size && size > ts->cfg.op_size) {
 470         units = (double) size / ts->cfg.op_size;
 471     }
 472
 473     for (i = 0; i < 2; i++) {
 474         LeakyBucket *bkt;
 475
 476         bkt = &ts->cfg.buckets[bucket_types_size[is_write][i]];
 477         bkt->level += size;
 478         if (bkt->burst_length > 1) {
 479             bkt->burst_level += size;
 480         }
 481
 482         bkt = &ts->cfg.buckets[bucket_types_units[is_write][i]];
 483         bkt->level += units;
 484         if (bkt->burst_length > 1) {
 485             bkt->burst_level += units;
 486         }
 487     }
 488 }
 489