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

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Date:	Thu, 7 Jan 2010 08:47:00 -0600
From:	Clark Williams <williams@...hat.com>
To:	Carsten Emde <Carsten.Emde@...dl.org>
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

On Thu, 07 Jan 2010 08:23:52 +0100
Carsten Emde <Carsten.Emde@...dl.org> wrote:

> 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.

I don't have a problem not having -d in the -S option. I was looking at
the possibility of synchronous sampling as well so it's probably a good
idea to keep it separate. 

The main things we want are implied -t, -a and -n.

Clark

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