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