Message-ID: <4B458C08.8070209@osadl.org>
Date: Thu, 07 Jan 2010 08:23:52 +0100
From: Carsten Emde <Carsten.Emde@osadl.org>
Organization: Open Source Automation Development Lab (OSADL) eG
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To: Clark Williams <williams@redhat.com>
CC: John Kacur <jkacur@redhat.com>, RT <linux-rt-users@vger.kernel.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] [rt-tests] change to cyclictest behavior
References: <20100106130400.7f30ae55@torg>	<520f0cf11001061139j2af13403qfcbf567647bdfaa8@mail.gmail.com>	<4B4502FD.1000404@osadl.org>	<20100106160434.77efc790@torg>	<4B450D91.7060403@osadl.org> <20100106162759.1d4d5b57@torg>
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Clark,

>> -S      --smp              Standard SMP testing (equals -a -t -n -d0),
>>                            same priority on all threads.
After having done some tests with a quickly hacked cyclictest version, I
have found an issue with including -d0. Apparently, small numbers make
life especially difficult for the scheduler; this is why we often used
-d1. Specifying -d0 seems a special case where all threads are in sync.
Maybe, we may miss some important latency constellations, if we do not
let the tasks slightly interfere. In any case, I would like to be able
to specify a distance _in addition_ to -S. This would create a scenario
where

  cyclictest -d1 -S

results in a distance of 0, and

  cyclictest -S -d1

results in a distance of 1. Would this be acceptable?

	Carsten.
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