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