linux-kernel - Re: Issues with Patch: "sched: Improve latencies and throughput"

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Message-Id: <1270150550.6413.27.camel@marge.simson.net>
Date:	Thu, 01 Apr 2010 21:35:50 +0200
From:	Mike Galbraith <efault@....de>
To:	Michael Grzeschik <mgr@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, rsc@...gutronix.de
Subject: Re: Issues with Patch: "sched: Improve latencies and throughput"

On Thu, 2010-04-01 at 10:43 +0200, Michael Grzeschik wrote:
> On Thu, Apr 01, 2010 at 07:49:46AM +0200, Mike Galbraith wrote:
> > On Thu, 2010-04-01 at 00:31 +0200, Michael Grzeschik wrote:
> > > We are using an arm mx31 embedded cpu with the v2.6.34 Kernelrelease and
> > > realized some issues with the scheduling behaviour the patch "sched:
> > > Improve latencies and throughput" [1] by Mike Galbraith introduced to
> > > the kernel.
> > > 
> > > When we used the alsa utility aplay to pipe some audio through an
> > > usbaudio device and put some scheduling overhead on the device, the
> > > amount of underruns, due to the not fast enough refilled ring buffer,
> > > was noticable increased with that patch [1] applied. Until we reverse
> > > applied the patch the amount of underruns was appreciable lower.
> > 
> > Testcase?
> 
> What we did was:
> 
> # Copy some audiofile to /dev/shm
> $ cp audiofile.wav /dev/shm
> 
> # Play that file with aplay in background
> $ aplay /dev/shm/auduifile.wav &
> 
> # Put some scheduling load on the system
> $ hackbench 6
> 
> We did use this on an MX31 from Freescale running with about 500 MHz and
> the generic usbaudio driver to play the audio throgh an C-Media USB
> audiodongle.

Hm.  I don't _think_ you've demonstrated a clear problem yet.

Q: how much CPU is aplay routinely using on this platform?

	-Mike

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