linux-kernel - Re: Scheduler accounting inflated for io bound processes.

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Date:	Tue, 25 Jun 2013 19:48:54 +0200
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Dave Chiluk <chiluk@...onical.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Scheduler accounting inflated for io bound processes.

On Tue, 2013-06-25 at 18:01 +0200, Mike Galbraith wrote: 
> On Thu, 2013-06-20 at 14:46 -0500, Dave Chiluk wrote: 
> > Running the below testcase shows each process consuming 41-43% of it's
> > respective cpu while per core idle numbers show 63-65%, a disparity of
> > roughly 4-8%.  Is this a bug, known behaviour, or consequence of the
> > process being io bound?
> 
> All three I suppose.

P.S.

perf top --sort=comm -C 3 -d 5 -F 250 (my tick freq)
56.65%    netserver
43.35%         pert

perf top --sort=comm -C 3 -d 5
67.16%  netserver
32.84%       pert

If you sample a high freq signal (netperf TCP_RR) at low freq (tick),
then try to reproduce the original signal, (very familiar) distortion
results.  Perf doesn't even care about softirq yada yada, so seems it's
a pure sample rate thing.

-Mike

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