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