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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH v2] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count
Cc: kosaki.motohiro@jp.fujitsu.com, balbir@linux.vnet.ibm.com,
       LKML <linux-kernel@vger.kernel.org>,
       Bharata B Rao <bharata@linux.vnet.ibm.com>,
       Balaji Rao <balajirrao@gmail.com>,
       Dhaval Giani <dhaval@linux.vnet.ibm.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>,
       Martin Schwidefsky <schwidefsky@de.ibm.com>
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> > >  	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?