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

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Message-ID: <4B543F65.4040803@linux.vnet.ibm.com>
Date:	Mon, 18 Jan 2010 16:30:53 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Anton Blanchard <anton@...ba.org>
CC:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	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 Monday 18 January 2010 03:25 PM, Anton Blanchard wrote:
> 
> Hi Martin,
> 
>> For s390 the jiffies_to_cputime is a compile time constant. No need to
>> initialize it at runtime, no? 
> 
> Indeed it is, I didn't look closely enough. Same with ia64 so no work to
> do on either arch :)
> 
>> The patch itself trades some accuracy (larger cpu accounting value that
>> are stored per-cpu) against runtime overhead (spinlock to transfer the
>> value to the global variable in __percpu_counter_add). Did you
>> calculate how big the loss in accuracy is?
> 
> The idea is we are already batching percpu_counter_batch jiffies, so
> with CONFIG_VIRT_CPU_ACCOUNTING we batch the equivalent amount in
> cputime.
> 

This patch worked well for me.

Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
Tested-by: Balbir Singh <balbir@...ux.vnet.ibm.com>

Balbir Singh.
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