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ratelimit: don't align wait time with slices 

It is possible for rate limited writes to keep overshooting a slice's
quota by a tiny amount causing the slice-aligned waiting period to
effectively halve the rate.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20180207071758.6818-1-w.bumiller@proxmox.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Wolfgang Bumiller 2018-02-07 08:17:58 +01:00 committed by Stefan Hajnoczi
parent 00d09fdbba
commit b7728f3221
1 changed files with 5 additions and 6 deletions
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11
include/qemu/ratelimit.h
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@ -36,7 +36,7 @@ typedef struct {
static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
{
int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
uint64_t delay_slices;
double delay_slices;
assert(limit->slice_quota && limit->slice_ns);
@ -55,12 +55,11 @@ static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
return 0;
}
/* Quota exceeded. Calculate the next time slice we may start
* sending data again. */
delay_slices = (limit->dispatched + limit->slice_quota - 1) /
limit->slice_quota;
/* Quota exceeded. Wait based on the excess amount and then start a new
* slice. */
delay_slices = (double)limit->dispatched / limit->slice_quota;
limit->slice_end_time = limit->slice_start_time +
delay_slices * limit->slice_ns;
(uint64_t)(delay_slices * limit->slice_ns);
return limit->slice_end_time - now;
}