linux-kernel - Re: [RFC] [rt-tests] change to cyclictest behavior

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Date:	Thu, 07 Jan 2010 08:23:52 +0100
From:	Carsten Emde <Carsten.Emde@...dl.org>
To:	Clark Williams <williams@...hat.com>
CC:	John Kacur <jkacur@...hat.com>,
	RT <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [rt-tests] change to cyclictest behavior

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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