linux-kernel - Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count

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Message-ID: <20090428103701.GE3825@in.ibm.com>
Date:	Tue, 28 Apr 2009 16:07:01 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Balaji Rao <balajirrao@...il.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	seto.hidetoshi@...fujitsu.com
Subject: Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu
	cputime count

On Tue, Apr 28, 2009 at 05:10:47PM +0900, KOSAKI Motohiro wrote:
> > On Tue, Apr 28, 2009 at 04:38:51PM +0900, KOSAKI Motohiro wrote:
> > > > On Tue, Apr 28, 2009 at 03:53:32PM +0900, KOSAKI Motohiro wrote:
> > > 
> > > > BTW, did you observe any real problem with the percpu counter spinlock ?
> > > 
> > > No.
> > > I review percpu_counter() caller recently and it seems stragen usage.
> > > 
> > 
> > I should have phrased the question better ...
> > 
> > So have you found any performance degradation with any benchmarks/workloads
> > on archs which define VIRT_CPU_ACCOUNTING due to percpu_counter spinlock
> > being taken on every tick ? If the answer is no, don't you think we could
> > wait before making the kind of change you are proposing ?
> 
> maybe, I don't understand your point.

My point is, let us not make this change if it is not a real problem that
has been observed on archs which define VIRT_CPU_ACCOUNTING.

Regards,
Bharata.
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