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

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Message-Id: <20090429110629.4B05.A69D9226@jp.fujitsu.com>
Date:	Wed, 29 Apr 2009 11:31:14 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	bharata@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com,
	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

> > > > > 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.

It's nice joke. but not constructive.

but another idea and another patch are always welcome.



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