include/qemu/throttle.h

   1 /*
   2  * QEMU throttling infrastructure
   3  *
   4  * Copyright (C) Nodalink, EURL. 2013-2014
   5  * Copyright (C) Igalia, S.L. 2015-2016
   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 #ifndef THROTTLE_H
  26 #define THROTTLE_H
  27
  28 #include "qemu-common.h"
  29 #include "qapi/qapi-types-block-core.h"
  30 #include "qemu/timer.h"
  31
  32 #define THROTTLE_VALUE_MAX 1000000000000000LL
  33
  34 typedef enum {
  35     THROTTLE_BPS_TOTAL,
  36     THROTTLE_BPS_READ,
  37     THROTTLE_BPS_WRITE,
  38     THROTTLE_OPS_TOTAL,
  39     THROTTLE_OPS_READ,
  40     THROTTLE_OPS_WRITE,
  41     BUCKETS_COUNT,
  42 } BucketType;
  43
  44 /*
  45  * This module implements I/O limits using the leaky bucket
  46  * algorithm. The code is independent of the I/O units, but it is
  47  * currently used for bytes per second and operations per second.
  48  *
  49  * Three parameters can be set by the user:
  50  *
  51  * - avg: the desired I/O limits in units per second.
  52  * - max: the limit during bursts, also in units per second.
  53  * - burst_length: the maximum length of the burst period, in seconds.
  54  *
  55  * Here's how it works:
  56  *
  57  * - The bucket level (number of performed I/O units) is kept in
  58  *   bkt.level and leaks at a rate of bkt.avg units per second.
  59  *
  60  * - The size of the bucket is bkt.max * bkt.burst_length. Once the
  61  *   bucket is full no more I/O is performed until the bucket leaks
  62  *   again. This is what makes the I/O rate bkt.avg.
  63  *
  64  * - The bkt.avg rate does not apply until the bucket is full,
  65  *   allowing the user to do bursts until then. The I/O limit during
  66  *   bursts is bkt.max. To enforce this limit we keep an additional
  67  *   bucket in bkt.burst_level that leaks at a rate of bkt.max units
  68  *   per second.
  69  *
  70  * - Because of all of the above, the user can perform I/O at a
  71  *   maximum of bkt.max units per second for at most bkt.burst_length
  72  *   seconds in a row. After that the bucket will be full and the I/O
  73  *   rate will go down to bkt.avg.
  74  *
  75  * - Since the bucket always leaks at a rate of bkt.avg, this also
  76  *   determines how much the user needs to wait before being able to
  77  *   do bursts again.
  78  */
  79
  80 typedef struct LeakyBucket {
  81     uint64_t avg;             /* average goal in units per second */
  82     uint64_t max;             /* leaky bucket max burst in units */
  83     double  level;            /* bucket level in units */
  84     double  burst_level;      /* bucket level in units (for computing bursts) */
  85     uint64_t burst_length;    /* max length of the burst period, in seconds */
  86 } LeakyBucket;
  87
  88 /* The following structure is used to configure a ThrottleState
  89  * It contains a bit of state: the bucket field of the LeakyBucket structure.
  90  * However it allows to keep the code clean and the bucket field is reset to
  91  * zero at the right time.
  92  */
  93 typedef struct ThrottleConfig {
  94     LeakyBucket buckets[BUCKETS_COUNT]; /* leaky buckets */
  95     uint64_t op_size;         /* size of an operation in bytes */
  96 } ThrottleConfig;
  97
  98 typedef struct ThrottleState {
  99     ThrottleConfig cfg;       /* configuration */
 100     int64_t previous_leak;    /* timestamp of the last leak done */
 101 } ThrottleState;
 102
 103 typedef struct ThrottleTimers {
 104     QEMUTimer *timers[2];     /* timers used to do the throttling */
 105     QEMUClockType clock_type; /* the clock used */
 106
 107     /* Callbacks */
 108     QEMUTimerCB *read_timer_cb;
 109     QEMUTimerCB *write_timer_cb;
 110     void *timer_opaque;
 111 } ThrottleTimers;
 112
 113 /* operations on single leaky buckets */
 114 void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta);
 115
 116 int64_t throttle_compute_wait(LeakyBucket *bkt);
 117
 118 /* init/destroy cycle */
 119 void throttle_init(ThrottleState *ts);
 120
 121 void throttle_timers_init(ThrottleTimers *tt,
 122                           AioContext *aio_context,
 123                           QEMUClockType clock_type,
 124                           QEMUTimerCB *read_timer_cb,
 125                           QEMUTimerCB *write_timer_cb,
 126                           void *timer_opaque);
 127
 128 void throttle_timers_destroy(ThrottleTimers *tt);
 129
 130 void throttle_timers_detach_aio_context(ThrottleTimers *tt);
 131
 132 void throttle_timers_attach_aio_context(ThrottleTimers *tt,
 133                                         AioContext *new_context);
 134
 135 bool throttle_timers_are_initialized(ThrottleTimers *tt);
 136
 137 /* configuration */
 138 bool throttle_enabled(ThrottleConfig *cfg);
 139
 140 bool throttle_is_valid(ThrottleConfig *cfg, Error **errp);
 141
 142 void throttle_config(ThrottleState *ts,
 143                      QEMUClockType clock_type,
 144                      ThrottleConfig *cfg);
 145
 146 void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg);
 147
 148 void throttle_config_init(ThrottleConfig *cfg);
 149
 150 /* usage */
 151 bool throttle_schedule_timer(ThrottleState *ts,
 152                              ThrottleTimers *tt,
 153                              bool is_write);
 154
 155 void throttle_account(ThrottleState *ts, bool is_write, uint64_t size);
 156 void throttle_limits_to_config(ThrottleLimits *arg, ThrottleConfig *cfg,
 157                                Error **errp);
 158 void throttle_config_to_limits(ThrottleConfig *cfg, ThrottleLimits *var);
 159
 160 #endif