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* QEMU throttling infrastructure
* Copyright (C) Nodalink, EURL. 2013-2014
* Copyright (C) Igalia, S.L. 2015-2016
* Authors:
* BenoƮt Canet <>
* Alberto Garcia <>
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 or
* (at your option) version 3 of the License.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <>.
#ifndef THROTTLE_H
#define THROTTLE_H
#include "qapi/qapi-types-block-core.h"
#include "qemu/timer.h"
#define THROTTLE_VALUE_MAX 1000000000000000LL
typedef enum {
} BucketType;
* This module implements I/O limits using the leaky bucket
* algorithm. The code is independent of the I/O units, but it is
* currently used for bytes per second and operations per second.
* Three parameters can be set by the user:
* - avg: the desired I/O limits in units per second.
* - max: the limit during bursts, also in units per second.
* - burst_length: the maximum length of the burst period, in seconds.
* Here's how it works:
* - The bucket level (number of performed I/O units) is kept in
* bkt.level and leaks at a rate of bkt.avg units per second.
* - The size of the bucket is bkt.max * bkt.burst_length. Once the
* bucket is full no more I/O is performed until the bucket leaks
* again. This is what makes the I/O rate bkt.avg.
* - The bkt.avg rate does not apply until the bucket is full,
* allowing the user to do bursts until then. The I/O limit during
* bursts is bkt.max. To enforce this limit we keep an additional
* bucket in bkt.burst_level that leaks at a rate of bkt.max units
* per second.
* - Because of all of the above, the user can perform I/O at a
* maximum of bkt.max units per second for at most bkt.burst_length
* seconds in a row. After that the bucket will be full and the I/O
* rate will go down to bkt.avg.
* - Since the bucket always leaks at a rate of bkt.avg, this also
* determines how much the user needs to wait before being able to
* do bursts again.
typedef struct LeakyBucket {
uint64_t avg; /* average goal in units per second */
uint64_t max; /* leaky bucket max burst in units */
double level; /* bucket level in units */
double burst_level; /* bucket level in units (for computing bursts) */
uint64_t burst_length; /* max length of the burst period, in seconds */
} LeakyBucket;
/* The following structure is used to configure a ThrottleState
* It contains a bit of state: the bucket field of the LeakyBucket structure.
* However it allows to keep the code clean and the bucket field is reset to
* zero at the right time.
typedef struct ThrottleConfig {
LeakyBucket buckets[BUCKETS_COUNT]; /* leaky buckets */
uint64_t op_size; /* size of an operation in bytes */
} ThrottleConfig;
typedef struct ThrottleState {
ThrottleConfig cfg; /* configuration */
int64_t previous_leak; /* timestamp of the last leak done */
} ThrottleState;
typedef struct ThrottleTimers {
QEMUTimer *timers[2]; /* timers used to do the throttling */
QEMUClockType clock_type; /* the clock used */
/* Callbacks */
QEMUTimerCB *read_timer_cb;
QEMUTimerCB *write_timer_cb;
void *timer_opaque;
} ThrottleTimers;
/* operations on single leaky buckets */
void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta);
int64_t throttle_compute_wait(LeakyBucket *bkt);
/* init/destroy cycle */
void throttle_init(ThrottleState *ts);
void throttle_timers_init(ThrottleTimers *tt,
AioContext *aio_context,
QEMUClockType clock_type,
QEMUTimerCB *read_timer_cb,
QEMUTimerCB *write_timer_cb,
void *timer_opaque);
void throttle_timers_destroy(ThrottleTimers *tt);
void throttle_timers_detach_aio_context(ThrottleTimers *tt);
void throttle_timers_attach_aio_context(ThrottleTimers *tt,
AioContext *new_context);
bool throttle_timers_are_initialized(ThrottleTimers *tt);
/* configuration */
bool throttle_enabled(ThrottleConfig *cfg);
bool throttle_is_valid(ThrottleConfig *cfg, Error **errp);
void throttle_config(ThrottleState *ts,
QEMUClockType clock_type,
ThrottleConfig *cfg);
void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg);
void throttle_config_init(ThrottleConfig *cfg);
/* usage */
bool throttle_schedule_timer(ThrottleState *ts,
ThrottleTimers *tt,
bool is_write);
void throttle_account(ThrottleState *ts, bool is_write, uint64_t size);
void throttle_limits_to_config(ThrottleLimits *arg, ThrottleConfig *cfg,
Error **errp);
void throttle_config_to_limits(ThrottleConfig *cfg, ThrottleLimits *var);