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SubjectRe: tbench regression with 2.6.32-rc1
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On Fri, 2009-10-09 at 12:16 +0200, Peter Zijlstra wrote:
> On Fri, 2009-10-09 at 17:51 +0800, Zhang, Yanmin wrote:
> > Comparing with 2.6.31's results, tebench has some regression with
> > 2.6.32-rc1.
> > COmmandline to start tbench:
> > #./tbench_srv &
> > #./tbench -t 600 CPU_NUM*2 127.0.0.1 #Use real cpu num to replace CPU_NUM
> > So start 2 client processes per cpu.
> >
> > 1) On 4*4 core tigerton: 30%;
> > 2) On 2*4 core stoakley: 15%;
> > 3) On 2*8 core Nehalem: 6%.
> >
> > As there are couple of patches which try to turn on/off some sched domain
> > flags such like SD_BALANCE_WAKE, I used some walkaround to bisect it.
> > On tigerton, below patch is captured.
> > commit 59abf02644c45f1591e1374ee7bb45dc757fcb88
> > Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Date: Wed Sep 16 08:28:30 2009 +0200
> >
> > sched: Add SD_PREFER_LOCAL
> >
> >
> > The patch reverting is not clean, so I did some testing by turning on/off
> > some domain flags and sched_feaures manually.
> >
> > 1) On tigerton: if SD_PREFER_LOCAL=0 (disable it), the regression becomes about 2%.
> > 2) On stoakley: if SD_PREFER_LOCAL=0 (disable it), the regression becomes about 4%.
> > 3) On Nehalem: Above method couldn't improve result. I'm still checking it.
> >
> > I also tried to turn on/off FAIR_SLEEPERS and GENTLE_FAIR_SLEEPERS. It seems they
> > has limited impact on tbench. I need double check these 2 flags.
>
> So the c2q cpus, and esp the one with smaller cache hurt from this. I
> guess we can turn this off without too much down sides. Maybe turn it on
> for NUMA on the nehalem?
I tested the patch and it does work like turning it off from domain flags.
So with the patch, stoakley still has 4% regression and tigerton has 2%.

>
>
> ---
> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index 25a9284..d823c24 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -143,6 +143,7 @@ extern unsigned long node_remap_size[];
> | 1*SD_BALANCE_FORK \
> | 0*SD_BALANCE_WAKE \
> | 1*SD_WAKE_AFFINE \
> + | 1*SD_PREFER_LOCAL \
> | 0*SD_SHARE_CPUPOWER \
> | 0*SD_POWERSAVINGS_BALANCE \
> | 0*SD_SHARE_PKG_RESOURCES \
> diff --git a/include/linux/topology.h b/include/linux/topology.h
> index fc0bf3e..57e6357 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -129,7 +129,7 @@ int arch_update_cpu_topology(void);
> | 1*SD_BALANCE_FORK \
> | 0*SD_BALANCE_WAKE \
> | 1*SD_WAKE_AFFINE \
> - | 1*SD_PREFER_LOCAL \
> + | 0*SD_PREFER_LOCAL \
> | 0*SD_SHARE_CPUPOWER \
> | 1*SD_SHARE_PKG_RESOURCES \
> | 0*SD_SERIALIZE \
> @@ -162,7 +162,7 @@ int arch_update_cpu_topology(void);
> | 1*SD_BALANCE_FORK \
> | 0*SD_BALANCE_WAKE \
> | 1*SD_WAKE_AFFINE \
> - | 1*SD_PREFER_LOCAL \
> + | 0*SD_PREFER_LOCAL \
> | 0*SD_SHARE_CPUPOWER \
> | 0*SD_SHARE_PKG_RESOURCES \
> | 0*SD_SERIALIZE \
>
>

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