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

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Message-ID: <20100401084311.GL10342@pengutronix.de>
Date:	Thu, 1 Apr 2010 10:43:11 +0200
From:	Michael Grzeschik <mgr@...gutronix.de>
To:	Mike Galbraith <efault@....de>
Cc:	linux-kernel@...r.kernel.org, rsc@...gutronix.de
Subject: Re: Issues with Patch: "sched: Improve latencies and throughput"

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.

Expected results with that patch:

underrun!!! (at least 323.946 ms long) < -- aplay
underrun!!! (at least 59.477 ms long)  < --     "
underrun!!! (at least 194.873 ms long) < --     "
Time: 7.048                            < -- hackbench
Time: 6.841                            < --     "
underrun!!! (at least 115.456 ms long) < -- aplay
underrun!!! (at least 37.849 ms long)  < --     "
underrun!!! (at least 588.637 ms long) < --     "
Time: 7.23                             < -- hackbench

results without the patch:

Time: 3.728                            < -- hackbench
underrun!!! (at least 58.557 ms long)  < -- aplay
Time: 3.771                            < -- hackbench
underrun!!! (at least 97.538 ms long)  < -- aplay
Time: 3.732                            < -- hackbench
Time: 3.630                            < --  ....
Time: 3.636
Time: 3.643

Thanks,
mgr

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