linux-kernel - Re: High priority threads causing severe CPU load imbalances

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Message-ID: <1270743344.20295.2554.camel@laptop>
Date:	Thu, 08 Apr 2010 18:15:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suresh Jayaraman <sjayaraman@...e.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Masayuki Igawa <igawa@....nes.nec.co.jp>
Subject: Re: High priority threads causing severe CPU load imbalances

On Tue, 2010-04-06 at 22:05 +0530, Suresh Jayaraman wrote:
> Perhaps there is a chance that with more CPUs, different number of high
> priority threads the problem could get worser as I mentioned above..?

One thing that could be happening (triggered by what Igawa-san said,
although his case is more complicated by involving the cgroup stuff) is
that f_b_g() ends up selecting a group that contains these niced tasks
and then f_b_q() will not find a suitable source queue because all of
them will have but a single runnable task on it and hence we simply
bail.

We'd somehow have to teach update_*_lb_stats() not to consider groups
where nr_running <= nr_cpus. I don't currently have a patch for that,
but I think that is the direction you might need to look in.

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