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

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Message-Id: <1185832234.3334.35.camel@josh-work.beaverton.ibm.com>
Date:	Mon, 30 Jul 2007 14:50:34 -0700
From:	Josh Triplett <josht@...ux.vnet.ibm.com>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
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

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

- Josh Triplett


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