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

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Message-ID: <48B6CFFD.2050801@qualcomm.com>
Date:	Thu, 28 Aug 2008 09:19:09 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	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

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 :).

I'm going to submit patches (soonish) that convert drivers/etc to use 
cancel_work_sync()/flush_work() instead of flush_scheduled_work().
That takes care of the
     "machine getting stuck because workqueue thread is starved"
case.

Max
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