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

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Date:	Wed, 06 Jan 2010 23:50:34 +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,

>> [..]
>> May I ask you to also include the -n option which is almost always
>> needed? This would then give:
>> -S      --smp              Standard SMP testing (equals -a -t -n -d0),
>>                            same priority on all threads.
> Yeah, you read my mind. How about -m (mlockall) as well?
Hmm, I think that this one is less obvious. Apparently, there are a
bunch of different opinions on mlockall(). I once heard, for example,
the opinion that mlockall() may - under some conditions - introduce a
performance penalty, but I did not verify that. Many real-time systems
do not have a "swap" line in /etc/fstab; mlockall() is not needed in
such systems. In addition, most today's systems have so much RAM that
swapping became a rather rare event. I hope some other RT-ers who are
more knowledgeable about memory management and swapping can comment on this.

Cyclictest was in use for years, before someone introduced the -m
option. I never used this option.

	Carsten.
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