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

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Date:	Tue, 12 May 2009 12:27:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	schwidefsky@...ibm.com, balajirrao@...il.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	bharata@...ux.vnet.ibm.com, tglx@...utronix.de,
	kamezawa.hiroyu@...fujitsu.com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter
	batch values for stats counters


* KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > > On Tue, 2009-05-12 at 19:01 +0900, KOSAKI Motohiro wrote:
> > > > +#ifdef CONFIGCONFIG_SMP
> > > 
> > > typo ?
> > 
> > yes, this week is my memorial stupid one ;)
> 
> ok, assemble list indicate current patch have no typo ;)
> 
> ffffffff814ae920:       48 c7 40 30 10 eb 2a    movq   $0xffffffff812aeb10,0x30(%rax)
> ffffffff814ae927:       81
> ffffffff814ae928:       c7 05 3e 37 fe ff 01    movl   $0x1,-0x1c8c2(%rip)        # ffffffff81492070 <scheduler_running>
> ffffffff814ae92f:       00 00 00
> ffffffff814ae932:       8b 05 28 52 fe ff       mov    -0x1add8(%rip),%eax        # ffffffff81493b60 <percpu_counter_batch>
> ffffffff814ae938:       89 05 36 37 fe ff       mov    %eax,-0x1c8ca(%rip)        # ffffffff81492074 <cpuacct_batch>
> ffffffff814ae93e:       41 5c                   pop    %r12
> 
> 
> 
> ---------------------------------------------------------
> Subject: [PATCH] cpuacct: Use bigger percpu counter batch values for stats counters on archs that have VIRT_CPU_ACCOUNTING=y
> 
> percpu counters used to accumulate statistics in cpuacct controller use
> the default batch value [max(2*nr_cpus, 32)] which can be too small for
> archs that define VIRT_CPU_ACCOUNTING. In such archs, a tick could result in
> cputime updates in the range of thousands. As a result, cpuacct_update_stats()
> would end up acquiring the percpu counter spinlock on every tick which
> is not good for performance.
> 
> Let those architectures to have a bigger batch threshold so that percpu counter
> spinlock isn't taken on every tick. This change doesn't affect the archs which
> don't define VIRT_CPU_ACCOUNTING and they continue to have the default
> percpu counter batch value.
> 
> Cc: Balaji Rao <balajirrao@...il.com>
> Cc: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  kernel/sched.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

Please reuse the commit log formatting fixes i did when i applied 
your patch. (you should still have that commit notification email)

	Ingo
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