linux-kernel - Re: [PATCH] better align percpu counter (Was Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

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Message-ID: <20090820100403.GB29093@elte.hu>
Date:	Thu, 20 Aug 2009 12:04:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Anton Blanchard <anton@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	balbir@...ux.vnet.ibm.com,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	schwidefsky@...ibm.com, balajirrao@...il.com,
	dhaval@...ux.vnet.ibm.com, tglx@...utronix.de,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] better align percpu counter (Was Re: [tip:sched/core]
	sched: cpuacct: Use bigger percpu counter batch values for stats
	counters


* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Thu, 20 Aug 2009 16:24:51 +1000
> Anton Blanchard <anton@...ba.org> wrote:
> 
> >  
> > Hi,
> > 
> > > Could you share contex-switch-test program ?
> > > I'd like to play with it to find out what I can do against percpu counter.
> > 
> > Sure:
> > 
> > http://ozlabs.org/~anton/junkcode/context_switch.c
> > 
> > Very simple, just run it once per core:
> > 
> > for i in `seq 0 31`
> > do
> > 	taskset -c $i ./context_switch &
> > done
> > 
> > Then look at the context switch rates in vmstat.
> > 
> Thank you for test program.
> 
> Before adjusting batch counter (I think you should modify it),
> Could you try this ?
> 
> I only have 8cpu(2socket) host but works well.
> (But...my host is x86-64 and has not virt-cpu-accouting.)
> 
> with your program
> before patch.
> cpuacct off : 414000-416000 ctsw per sec.
> cpuacct on  : 401000-404000 ctsw per sec.
> 
> after patch
> cpuacct on  : 412000-413000 ctsw per sec.
> 
> Maybe I should check cache-miss late ;)

Btw., in latest upstream you can do that via:

  cd tools/perf/
  make -j install

  perf stat --repeat 5 -- taskset -c 1 ./context_switch

there will be cache-miss and other stats, error bars so 
you can compare the before/after better, etc.

	Ingo
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