linux-kernel - Re: [PATCH RT] Fix RT balancing tasks pulling

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Date:	Tue, 31 Jul 2007 13:48:24 +0200
From:	Sébastien Dugué <sebastien.dugue@...l.net>
To:	Josh Triplett <josht@...ux.vnet.ibm.com>
Cc:	Linux RT Users <linux-rt-users@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>,
	Darren Hart <dvhltc@...ibm.com>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH RT] Fix RT balancing tasks pulling


  Hi Josh,

On Mon, 30 Jul 2007 14:50:34 -0700 Josh Triplett <josht@...ux.vnet.ibm.com> wrote:

> On Tue, 2007-07-24 at 15:42 +0200, Sébastien Dugué wrote:
> >   this one-liner fixes a bug in balance_rt_tasks() which sometimes manifests by
> > having a lower prio task being scheduled while a higher prio task is sitting
> > waiting on another runqueue.
> > 
> >   This is pretty hard to reproduce on low cpu count machines, for example, I
> > had to have sched_football run in a loop for ~38h before it failed on a dual HT
> > Xeon box.
> 
> Very impressive find, and this does seem to improve things in some
> cases.
> 
> However, with 2.6.22.1-rt8, which includes this patch, I still managed
> to get some failures after a few hours on an 8-way (quad dual-core) box.
> Preliminary results so far:
>     420 Final ball position: 0
>       2 Final ball position: 1
> 

  Darn, I thought it was it :(

  I had a ~60h run on my box with the very same kernel without a single
failure.

  Do you have any other user RT load running when those failures pop up?

  Anyway, back to scheduler code dissection now.

  Sébastien.
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