Re: oltp ~10% regression with 2.6.27-rc5 on stoakley machine
From: Peter Zijlstra
Date: Thu Sep 04 2008 - 06:12:46 EST
On Thu, 2008-09-04 at 16:51 +0800, Lin Ming wrote:
> Comparing with 2.6.27-rc4, oltp has ~10% regression with 2.6.27-rc5 on
> 8-core stoakley machine.
>
> Run oltp with 8 threads 120 seconds, vmstat shows much more idle time, about ~30%
>
> procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
> r b swpd free buff cache si so bi bo in cs us sy id wa st
> 10 0 0 7822824 42240 123740 0 0 312 47 442 1613 3 2 88 6 0
> 9 0 0 7822312 42240 123764 0 0 0 16 26691 232566 56 14 30 0 0
> 13 0 0 7821940 42240 123764 0 0 0 16 26661 228689 54 14 32 0 0
> 8 0 0 7821320 42240 123764 0 0 0 16 31508 263765 61 17 23 0 0
> 12 0 0 7820948 42240 123764 0 0 16 16 28666 242402 57 15 28 0 0
> 9 0 0 7820584 42240 123780 0 0 0 16 27107 230804 56 14 30 0 0
> 10 0 0 7819964 42240 123796 0 0 16 612 27599 244037 55 16 29 0 0
> 11 0 0 7819356 42240 123796 0 0 0 64 23540 209713 51 13 36 0 0
> 10 0 0 7819212 42240 123796 0 0 0 32 25674 224205 54 13 32 0 0
> 10 0 0 7818716 42240 123796 0 0 0 20 30106 257161 59 16 25 0 0
> 7 0 0 7818468 42240 123796 0 0 0 16 28356 241551 57 14 29 0 0
> 10 0 0 7818096 42240 123796 0 0 0 16 39174 273656 64 16 20 0 0
> 12 0 0 7817724 42240 123796 0 0 0 20 39688 276936 63 16 20 0 0
> 11 0 0 7817352 42240 123796 0 0 0 16 42543 285192 66 16 18 0 0
> 9 0 0 7817352 42240 123796 0 0 0 16 37083 259830 62 14 24 0 0
> 8 0 0 7817104 42240 123796 0 0 0 16 37450 259160 61 15 23 0 0
> 10 0 0 7816516 42240 123796 0 0 0 64 37425 261870 61 16 23 0 0
> 11 0 0 7815896 42240 123812 0 0 16 16 41558 279320 66 16 18 0 0
> 9 0 0 7815648 42240 123812 0 0 0 16 34017 235741 59 14 28 0 0
> 10 0 0 7815152 42240 123812 0 0 0 16 35642 248888 60 14 26 0 0
> 9 0 0 7814532 42240 123812 0 0 0 16 38517 263220 63 15 22 0 0
> 9 0 0 7814160 42240 123812 0 0 0 20 35965 246487 61 14 25 0 0
> 10 0 0 7814036 42240 123812 0 0 0 16 33852 236313 59 13 28 0 0
> 11 0 0 7813664 42240 123812 0 0 0 16 34958 244819 59 14 27 0 0
> 10 0 0 7813416 42240 123812 0 0 0 16 26106 202062 53 10 37 0 0
> 10 0 0 7812672 42240 123812 0 0 0 16 31174 222714 56 12 32 0 0
> 9 0 0 7812300 42240 123812 0 0 0 276 25089 196813 52 11 38 0 0
> 9 0 0 7812060 42240 123812 0 0 0 16 31877 228004 57 12 31 0 0
>
>
>
> Bisect located below patch,
> after reverted this patch the regression disappear.
>
> commit 354879bb977e06695993435745f06a0f6d39ce2b
> Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Date: Mon Aug 25 17:15:34 2008 +0200
>
> sched_clock: fix cpu_clock()
>
> This patch fixes 3 issues:
>
> a) it removes the dependency on jiffies, because jiffies are
> incremented
> by a single CPU, and the tick is not synchronized between CPUs.
> Therefore
> relying on it to calculate a window to clip whacky TSC values
> doesn't work
> as it can drift around.
>
> So instead use [GTOD, GTOD+TICK_NSEC) as the window.
>
> b) __update_sched_clock() did (roughly speaking):
>
> delta = sched_clock() - scd->tick_raw;
> clock += delta;
>
> Which gives exponential growth, instead of linear.
>
> c) allows the sched_clock_cpu() value to warp the u64 without
> breaking.
>
> the results are more reliable sched_clock() deltas:
Thats bizarre... that just indicates the better clock, which should give
better (read fairer) scheduling hurts your workload.
Is there anything I can run to see if we can fix the scheduler perhaps?
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