Message-ID: <1372182534.7497.129.camel@marge.simpson.net>
Subject: Re: Scheduler accounting inflated for io bound processes.
From: Mike Galbraith <bitbucket@online.de>
To: Dave Chiluk <chiluk@canonical.com>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
Date: Tue, 25 Jun 2013 19:48:54 +0200
In-Reply-To: <1372176104.7497.86.camel@marge.simpson.net>
References: <51C35C05.1070005@canonical.com>
	 <1372176104.7497.86.camel@marge.simpson.net>
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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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