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fix #1642: merge: ratelimit: don't align wait time with slices

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Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
This commit is contained in:
Wolfgang Bumiller 2018-02-07 16:39:07 +01:00
parent ec24bd7a23
commit 22ea5045c3
2 changed files with 48 additions and 0 deletions
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47
debian/patches/extra/0035-ratelimit-don-t-align-wait-time-with-slices.patch vendored Normal file
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@ -0,0 +1,47 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Wolfgang Bumiller <w.bumiller@proxmox.com>
Date: Tue, 6 Feb 2018 11:34:34 +0100
Subject: [PATCH] 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>
---
include/qemu/ratelimit.h | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
index 8da1232574..324ff04fe2 100644
--- a/include/qemu/ratelimit.h
+++ b/include/qemu/ratelimit.h
@@ -35,7 +35,7 @@ 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);
@@ -54,12 +54,11 @@ 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;
}
--
2.11.0

1
debian/patches/series vendored
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@ -61,3 +61,4 @@ extra/0031-i386-Add-support-for-SPEC_CTRL-MSR.patch
extra/0032-i386-Add-spec-ctrl-CPUID-bit.patch
extra/0033-i386-Add-FEAT_8000_0008_EBX-CPUID-feature-word.patch
extra/0034-i386-Add-new-IBRS-versions-of-Intel-CPU-models.patch
extra/0035-ratelimit-don-t-align-wait-time-with-slices.patch