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throttle: Add support for burst periods

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This patch adds support for burst periods to the throttling code.
With this feature the user can keep performing bursts as defined by
the LeakyBucket.max rate for a configurable period of time.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Alberto Garcia 2016-02-18 12:27:01 +02:00 committed by Kevin Wolf
parent 1588ab5d0b
commit 100f8f2608
2 changed files with 97 additions and 19 deletions
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41
include/qemu/throttle.h
View File

@ -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>
@ -42,16 +42,47 @@ 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

75
util/throttle.c
View File

@ -41,6 +41,14 @@ void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta_ns)
/* make the bucket leak */
bkt->level = MAX(bkt->level - leak, 0);
/* if we allow bursts for more than one second we also need to
* keep track of bkt->burst_level so the bkt->max goal per second
* is attained */
if (bkt->burst_length > 1) {
leak = (bkt->max * (double) delta_ns) / NANOSECONDS_PER_SECOND;
bkt->burst_level = MAX(bkt->burst_level - leak, 0);
}
}
/* Calculate the time delta since last leak and make proportionals leaks
@ -91,13 +99,24 @@ int64_t throttle_compute_wait(LeakyBucket *bkt)
return 0;
}
extra = bkt->level - bkt->max;
if (extra <= 0) {
return 0;
/* If the bucket is full then we have to wait */
extra = bkt->level - bkt->max * bkt->burst_length;
if (extra > 0) {
return throttle_do_compute_wait(bkt->avg, extra);
}
return throttle_do_compute_wait(bkt->avg, extra);
/* If the bucket is not full yet we have to make sure that we
* fulfill the goal of bkt->max units per second. */
if (bkt->burst_length > 1) {
/* We use 1/10 of the max value to smooth the throttling.
* See throttle_fix_bucket() for more details. */
extra = bkt->burst_level - bkt->max / 10;
if (extra > 0) {
return throttle_do_compute_wait(bkt->max, extra);
}
}
return 0;
}
/* This function compute the time that must be waited while this IO
@ -177,7 +196,11 @@ void throttle_timers_attach_aio_context(ThrottleTimers *tt,
*/
void throttle_config_init(ThrottleConfig *cfg)
{
unsigned i;
memset(cfg, 0, sizeof(*cfg));
for (i = 0; i < BUCKETS_COUNT; i++) {
cfg->buckets[i].burst_length = 1;
}
}
/* To be called first on the ThrottleState */
@ -301,6 +324,16 @@ bool throttle_is_valid(ThrottleConfig *cfg, Error **errp)
return false;
}
if (!cfg->buckets[i].burst_length) {
error_setg(errp, "the burst length cannot be 0");
return false;
}
if (cfg->buckets[i].burst_length > 1 && !cfg->buckets[i].max) {
error_setg(errp, "burst length set without burst rate");
return false;
}
if (cfg->buckets[i].max && !cfg->buckets[i].avg) {
error_setg(errp, "bps_max/iops_max require corresponding"
" bps/iops values");
@ -317,7 +350,7 @@ static void throttle_fix_bucket(LeakyBucket *bkt)
double min;
/* zero bucket level */
bkt->level = 0;
bkt->level = bkt->burst_level = 0;
/* The following is done to cope with the Linux CFQ block scheduler
* which regroup reads and writes by block of 100ms in the guest.
@ -420,22 +453,36 @@ bool throttle_schedule_timer(ThrottleState *ts,
*/
void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
{
const BucketType bucket_types_size[2][2] = {
{ THROTTLE_BPS_TOTAL, THROTTLE_BPS_READ },
{ THROTTLE_BPS_TOTAL, THROTTLE_BPS_WRITE }
};
const BucketType bucket_types_units[2][2] = {
{ THROTTLE_OPS_TOTAL, THROTTLE_OPS_READ },
{ THROTTLE_OPS_TOTAL, THROTTLE_OPS_WRITE }
};
double units = 1.0;
unsigned i;
/* if cfg.op_size is defined and smaller than size we compute unit count */
if (ts->cfg.op_size && size > ts->cfg.op_size) {
units = (double) size / ts->cfg.op_size;
}
ts->cfg.buckets[THROTTLE_BPS_TOTAL].level += size;
ts->cfg.buckets[THROTTLE_OPS_TOTAL].level += units;
for (i = 0; i < 2; i++) {
LeakyBucket *bkt;
if (is_write) {
ts->cfg.buckets[THROTTLE_BPS_WRITE].level += size;
ts->cfg.buckets[THROTTLE_OPS_WRITE].level += units;
} else {
ts->cfg.buckets[THROTTLE_BPS_READ].level += size;
ts->cfg.buckets[THROTTLE_OPS_READ].level += units;
bkt = &ts->cfg.buckets[bucket_types_size[is_write][i]];
bkt->level += size;
if (bkt->burst_length > 1) {
bkt->burst_level += size;
}
bkt = &ts->cfg.buckets[bucket_types_units[is_write][i]];
bkt->level += units;
if (bkt->burst_length > 1) {
bkt->burst_level += units;
}
}
}