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

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Date:	Mon, 18 Jan 2010 09:34:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Anton Blanchard <anton@...ba.org>
Cc:	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Balbir Singh <balbir@...ux.vnet.ibm.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,
	kamezawa.hiroyu@...fujitsu.com, akpm@...ux-foundation.org,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>, linux390@...ibm.com
Subject: Re: [PATCH] sched: cpuacct: Use bigger percpu counter batch values
 for stats counters

On Mon, 2010-01-18 at 19:21 +1100, Anton Blanchard wrote:
> Hi Peter,
> 
> > Seems like a good idea, but isn't that batch number rather static? If
> > so, computing it in some init path would save that multiply on the
> > actual accounting path.
> 
> It is mostly static, but percpu_counter_batch does change with hotplug
> operations. Adding a hotplug notifier felt like a lot of work but I was
> worried we have issues if we didn't scale with hotplug add operations.

OK, trading a notifier for a mult might be worth it, we'll see if
someone complains ;-)

Lets got with this for now.

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