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