linux-kernel - Re: High priority tasks break SMP balancer?

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Message-ID: <Pine.LNX.4.64.0711151830260.31691@schroedinger.engr.sgi.com>
Date:	Thu, 15 Nov 2007 18:31:49 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Micah Dowty <micah@...are.com>
cc:	Kyle Moffett <mrmacman_g4@....com>,
	Cyrus Massoumi <cyrusm@....net>,
	LKML Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...l.org>,
	Mike Galbraith <efault@....de>, Paul Menage <menage@...gle.com>
Subject: Re: High priority tasks break SMP balancer?

On Thu, 15 Nov 2007, Micah Dowty wrote:

> On all kernels I've tested from after your patch was committed, I can
> reproduce a problem where a single high-priority thread which wakes up
> very frequently can artificially inflate the SMP balancer's load
> average for one CPU, causing other tasks to be migrated off that
> CPU. The result is that this high-priority thread (which may only use
> a few percent CPU) gets an entire CPU to itself. Even if there are
> several busy-looping threads running, this CPU will be mostly idle.

I am a bit at a loss as to how this could relate to the patch. This looks 
like a load balance logic issue that causes the load calculation to go 
wrong?


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