linux-kernel - Re: [PATCH 6/6] sched: disabled rt-bandwidth by default

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Date:	Thu, 28 Aug 2008 14:00:53 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <nickpiggin@...oo.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Stefani Seibold <stefani@...bold.net>,
	Dario Faggioli <raistlin@...ux.it>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 6/6] sched: disabled rt-bandwidth by default

On Thu, 2008-08-28 at 13:50 +0200, Andi Kleen wrote:
> On Thu, Aug 28, 2008 at 01:19:13PM +0200, Peter Zijlstra wrote:
> > On Thu, 2008-08-28 at 13:09 +0200, Andi Kleen wrote:
> > > > Even if the system has multiple CPUs, and even if just a single CPU is 
> > > > fully utilized by an RT task, without the rt-limit the system will still 
> > > > lock up in practice due to various other factors: workqueues and tasks 
> > > > being 'stuck' on CPUs that host an RT hog. 
> > > 
> > > The load balancer will not notice that a particular CPU is busy
> > > with real time tasks?
> > 
> > Not currently, working on that though.
> 
> I wonder if it would make sense to break affinities in extreme case?
> With that even the workqueues would work again.

Then people can no longer assume stuff like queue_work_on() etc.. works.
Users of such code might depend on it actually running on the specified
cpu.



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