linux-kernel - Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for CPU"

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Message-ID: <20091005072428.16ce40e4@infradead.org>
Date:	Mon, 5 Oct 2009 07:24:28 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Frans Pop <elendil@...net.nl>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-wireless@...r.kernel.org
Subject: Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for
 CPU"

On Mon, 5 Oct 2009 16:13:31 +0200
Frans Pop <elendil@...net.nl> wrote:

> On Monday 05 October 2009, Frans Pop wrote:
> > With .32-rc3 I'm getting occasional skips from amarok while playing
> > music from an NFS share (3 today so far), something I've not had in
> > a long time.
> >
> > The reason looks to be that latencytop consistently shows 'iwlagn'
> > as the top affected process with "Scheduler: waiting for CPU".
> > Values of 100-140 ms occur frequently, but I've also seen higher
> > values (180, 207). I don't remember seeing iwlagn high in the list
> > before, but I have not checked earlier kernels yet.
> >
> > Added to that 'phy0' also frequently shows high with values of
> > 25-75 ms.
> >
> > The system is otherwise essentially idle. Other processes typically
> > show a latency < 5 ms.
> 
> If I give the system some work to do (like compiling a kernel), the 
> latencies on iwlagn and phy0 disappear (values < 5 ms).
> Is this related to ondemand frequency scaling?

shouldn't be.... but

can you do a 5 second or so timechart recording of this?
That will capture all scheduler delays as well as the P states etc....

(to do a timechart recording, first make sure debugfs is mounted, and
then do in tools/perf 

./perf timechart record sleep 5

then you can turn it into an SVG with

./perf timechart

)


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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