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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Oliver.Neukum@lrz.uni-muenchen.de, yodaiken@fsmlabs.com,
        phillips@bonn-fries.net (Daniel Phillips),
        arjan@fenrus.demon.nl (Arjan van de Ven),
        zippel@linux-m68k.org (Roman Zippel), linux-kernel@vger.kernel.org
Subject: Re: [2.4.17/18pre] VM and swap - it's really unusable
In-Reply-To: <E16QB8b-0002K8-00@the-village.bc.nu>
From: Momchil Velikov <velco@fadata.bg>
In-Reply-To: <E16QB8b-0002K8-00@the-village.bc.nu>
Date: 15 Jan 2002 00:34:01 +0200
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>>>>> "Alan" == Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

Oliver> You can have an rt task block on a lock held by a normal task that was 
Oliver> preempted by a rt task of lower priority. The same problem as with the 
Oliver> sched_idle patches.
>> 
>> This can happen with a non-preemptible kernel too. And it has nothing to
>> do with scheduling policy.

Alan> So why bother adding pre-emption. As you keep saying - it doesnt
Alan> gain anything

Nope. I don't. I said (at least in the above) it didn't hurt.

One can consider a non-preemptible kernel as a special kind of
priority inversion, preemptible kernel will eliminate _that_ case of
priority inversion.

Regards,
-velco

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