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Subject: Re: [PATCH 5/6] sched: SCHED_FIFO/SCHED_RR watchdog timer
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Mike Galbraith <efault@gmx.de>,
       Dmitry Adamushko <dmitry.adamushko@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Lennart Poettering <mzxreary@0pointer.de>
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References: <20071031211030.310581000@chello.nl>
	 <20071031211249.531637000@chello.nl>  <p73fxzr2bv4.fsf@bingen.suse.de>
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Date: Wed, 31 Oct 2007 23:03:28 +0100
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On Wed, 2007-10-31 at 22:49 +0100, Andi Kleen wrote:
> Peter Zijlstra <a.p.zijlstra@chello.nl> writes:
> 
> > Introduce a new rlimit that allows the user to set a runtime timeout
> > on real-time tasks. Once this limit is exceeded the task will receive
> > SIGXCPU.
> 
> Nice idea.
> 
> It would be even nicer if you could allow a couple of them. Partition
> the RT priorities into a few classes and have an own limit for each them.
> 
> A small number of classes (3-4) would be probably enough and not bloat
> the rlimits too much.
> 
> I'm thinking of the case where you have different kinds of real
> time processes. Like your mp3 player which you want to be slightly
> real time, but with a low SIGXCPU limit. 
> 
> And then something else real time which is more important and
> you would set a higher limit. etc.

But its an rlimit, it can be set per process. Not sure what multiple
classes per process would gain us, let alone how that process has to
figure out which class to use.