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

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Message-ID: <20080828163318.GR26610@one.firstfloor.org>
Date:	Thu, 28 Aug 2008 18:33:19 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Max Krasnyansky <maxk@...lcomm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefani Seibold <stefani@...bold.net>,
	Dario Faggioli <raistlin@...ux.it>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 6/6] sched: disabled rt-bandwidth by default

On Thu, Aug 28, 2008 at 06:25:48PM +0200, Ingo Molnar wrote:
> 
> * Max Krasnyansky <maxk@...lcomm.com> wrote:
> 
> > 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.
> >
> > Please lets not break affinity :).
> 
> correct, breaking affinity is a rather stupid idea.

Ok let's remove cpu hotunplug then.  Probably nobody uses it anyways @)

Seriously cpu affinity on all non BP CPU is currently broken on every
suspend to RAM, doing it in a few more cases when it makes the system
more robust is unlikely to hurt anybody.

-Andi

-- 
ak@...ux.intel.com

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