linux-kernel - Re: [PATCH v2] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count

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Message-ID: <20090430090200.GF4430@balbir.in.ibm.com>
Date:	Thu, 30 Apr 2009 14:32:00 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Balaji Rao <balajirrao@...il.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH v2] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu
	cputime count

* KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-04-30 17:52:16]:

> > > >  	for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
> > > > -		s64 val = percpu_counter_read(&ca->cpustat[i]);
> > > > +		s64 val = percpu_counter_sum(&ca->cpustat[i]);
> > > >  		val = cputime64_to_clock_t(val);
> > > >  		cb->fill(cb, cpuacct_stat_desc[i], val);
> > > >  	}
> > > 
> > > What do the test results look like with this? I'll see if I can find
> > > some time to test this patch. On a patch read level this seems much better
> > > to me, Peter?
> > 
> > I don't really fancy percpu_counter_sum() usage. I'm thinking its ok to
> > degrate accuracy on larger machines and simply use
> > percpu_counter_read().
> 
> I have same opinion with peter. Balbir, What do you think?
>

Sure, but the larger the delta gets, the less useful the metric gets
:) I am OK with going back to percpu_counter_read() if that is the
consensus. 

-- 
	Balbir
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