diff options
Diffstat (limited to 'qemu/include/qemu/throttle.h')
| -rw-r--r-- | qemu/include/qemu/throttle.h | 56 |
1 files changed, 41 insertions, 15 deletions
diff --git a/qemu/include/qemu/throttle.h b/qemu/include/qemu/throttle.h index 995b2d595..910965760 100644 --- a/qemu/include/qemu/throttle.h +++ b/qemu/include/qemu/throttle.h @@ -2,7 +2,7 @@ * QEMU throttling infrastructure * * Copyright (C) Nodalink, EURL. 2013-2014 - * Copyright (C) Igalia, S.L. 2015 + * Copyright (C) Igalia, S.L. 2015-2016 * * Authors: * Benoît Canet <benoit.canet@nodalink.com> @@ -25,10 +25,11 @@ #ifndef THROTTLE_H #define THROTTLE_H -#include <stdint.h> #include "qemu-common.h" #include "qemu/timer.h" +#define THROTTLE_VALUE_MAX 1000000000000000LL + typedef enum { THROTTLE_BPS_TOTAL, THROTTLE_BPS_READ, @@ -40,16 +41,47 @@ typedef enum { } BucketType; /* - * The max parameter of the leaky bucket throttling algorithm can be used to - * allow the guest to do bursts. - * The max value is a pool of I/O that the guest can use without being throttled - * at all. Throttling is triggered once this pool is empty. + * 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_length 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 { double avg; /* average goal in units per second */ double max; /* leaky bucket max burst in units */ double level; /* bucket level in units */ + double burst_level; /* bucket level in units (for computing bursts) */ + unsigned burst_length; /* max length of the burst period, in seconds */ } LeakyBucket; /* The following structure is used to configure a ThrottleState @@ -82,12 +114,6 @@ void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta); int64_t throttle_compute_wait(LeakyBucket *bkt); -/* expose timer computation function for unit tests */ -bool throttle_compute_timer(ThrottleState *ts, - bool is_write, - int64_t now, - int64_t *next_timestamp); - /* init/destroy cycle */ void throttle_init(ThrottleState *ts); @@ -110,9 +136,7 @@ bool throttle_timers_are_initialized(ThrottleTimers *tt); /* configuration */ bool throttle_enabled(ThrottleConfig *cfg); -bool throttle_conflicting(ThrottleConfig *cfg); - -bool throttle_is_valid(ThrottleConfig *cfg); +bool throttle_is_valid(ThrottleConfig *cfg, Error **errp); void throttle_config(ThrottleState *ts, ThrottleTimers *tt, @@ -120,6 +144,8 @@ void throttle_config(ThrottleState *ts, void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg); +void throttle_config_init(ThrottleConfig *cfg); + /* usage */ bool throttle_schedule_timer(ThrottleState *ts, ThrottleTimers *tt, |