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Date: Thu, 21 Jan 2010 20:55:39 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
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To: Anton Blanchard <anton@samba.org>
CC: Martin Schwidefsky <schwidefsky@de.ibm.com>,
       Bharata B Rao <bharata@linux.vnet.ibm.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>, mingo@redhat.com, hpa@zytor.com,
       linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl,
       balajirrao@gmail.com, dhaval@linux.vnet.ibm.com, tglx@linutronix.de,
       kamezawa.hiroyu@jp.fujitsu.com, akpm@linux-foundation.org,
       Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com
Subject: Re: [PATCH] sched: cpuacct: Use bigger percpu counter batch values
 for stats counters
References: <20090512102412.GG6351@balbir.in.ibm.com> <20090512102939.GB11714@elte.hu> <20090512193656.D647.A69D9226@jp.fujitsu.com> <20090716081010.GB3134@in.ibm.com> <20090716083948.GA2950@kryten> <20090820051038.GF21100@kryten> <20100118044142.GS12666@kryten> <20100118104213.64231c1e@mschwide.boeblingen.de.ibm.com> <20100118095527.GV12666@kryten>
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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.
> 

Hi, Peter, Ingo

Could we please pick up the patch for -tip?

-- 
Three Cheers,
Balbir Singh