diff options
| -rw-r--r-- | include/qemu/throttle.h | 41 | ||||
| -rw-r--r-- | util/throttle.c | 73 |
2 files changed, 96 insertions, 18 deletions
diff --git a/include/qemu/throttle.h b/include/qemu/throttle.h index 8ec8951225..63df69070a 100644 --- a/include/qemu/throttle.h +++ b/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> @@ -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 diff --git a/util/throttle.c b/util/throttle.c index 6a01cee892..371c769455 100644 --- a/util/throttle.c +++ b/util/throttle.c @@ -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 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); + } - if (extra <= 0) { - return 0; + /* 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 throttle_do_compute_wait(bkt->avg, 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; + + bkt = &ts->cfg.buckets[bucket_types_size[is_write][i]]; + bkt->level += size; + if (bkt->burst_length > 1) { + bkt->burst_level += size; + } - 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_units[is_write][i]]; + bkt->level += units; + if (bkt->burst_length > 1) { + bkt->burst_level += units; + } } } |