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

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Date:	Mon, 5 Oct 2009 16:13:31 +0200
From:	Frans Pop <elendil@...net.nl>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	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 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?
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