linux-kernel - Re: [PATCH] sched: Improve latencies under load by decreasing minimum

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Date:	Sat, 18 Sep 2010 10:53:01 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Matthias Dahl <ml_kernel@...tal-soul.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] sched: Improve latencies under load by decreasing
	minimum

* Matthias Dahl (ml_kernel@...tal-soul.de) wrote:
> Hi.
> 
> I don't know if this is relevant but I just tried this ontop 2.6.35.4 while
> investigating a different problem and it was quite easy to produce audio
> buffer underruns while doing some compile job in the background.
> 
> To be exact: I had vlc (1.1 git) play back several flac files and was compiling
> qt 4.7 in the background as a test w/ -j5 on an i7 860 . The result was that w/
> the decreased granularity it caused noticeable audio buffer underruns while it
> worked just fine w/ the default granularity (nothing else touched).
> 
> Just wanted to report this early on and hope it helps.

Hi Matthias,

Thanks for reporting this. I have a few more questions:

Can you provide:

you full kernel .config

The config values of your sound card:

cat /proc/asound/card0/pcm0p/sub0/hw_params
cat /proc/asound/card0/pcm0c/sub0/hw_params

while you play your audio. (could be other than pcm0p, try to get one which is
not "Closed" while you play) Also providing the dmesg output showing which sound
card driver you are using might help.

Also the output of:
cat /proc/cpuinfo

Also, can you try reproducing the problem with different players ? With
non-git-bleeding-edge vlc versions too ? Can you reproduce this problem while
using "aplay" (a much simpler player) to play wav files ? (I've got an
instrumented version hooked on my tracer that traces underruns in here).

Thanks !

Mathieu

> 
> So long,
> matthias.
> 
> PS. Please cc' as I am not subscribed. Thanks a lot.

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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