linux-kernel - Re: Kernel migration eat CPUs

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Date:	Thu, 5 Sep 2013 13:12:52 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexey Vlasov <renton@...ton.name>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Mike Galbraith <bitbucket@...ine.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Kernel migration eat CPUs


* Alexey Vlasov <renton@...ton.name> wrote:

> On Sun, Aug 25, 2013 at 04:28:37PM +0200, Peter Zijlstra wrote:
> 
> > and a function (or function-graph)
> > trace for when this happens?
> 
> Unfortunately I could not make trace.
> First when migration threads start to eat CPUs and when I turn on trace:
> # echo function > current_tracer
> # echo 1 > tracing_on
> then server is down at once. LA comes up to several thousands, it stops
> to receive commands. Sometimes I even have to reboot it.

Could you try the latest -tip tree at:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

In particular this fix:

   5a8e01f8fa51 sched/cputime: Do not scale when utime == 0

Could perhaps fix the phantom CPU overhead you are seeing?

Thanks,

	Ingo
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