linux-kernel - Re: [Alsa-user] new source of MIDI playback slow-down identified - 5a03b051ed87e72b959f32a86054e1142ac4cf55 thp: use compaction in kswapd for GFP

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Date:	Wed, 23 Feb 2011 22:25:41 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Arthur Marsh <arthur.marsh@...ernode.on.net>
Cc:	Clemens Ladisch <cladisch@...glemail.com>,
	alsa-user@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [Alsa-user] new source of MIDI playback slow-down identified -
 5a03b051ed87e72b959f32a86054e1142ac4cf55 thp: use compaction in kswapd for
 GFP_ATOMIC order > 0

On Thu, Feb 24, 2011 at 06:37:58AM +1030, Arthur Marsh wrote:
> kswapd-high_wmark + compaction-kswapd-2 - kswapd0 CPU up to 11 percent 
> and slightly less pronounced slowdowns of MIDI playback compared to 
> previous patches.
> 
> kswapd-high_wmark + compaction-no-kswapd-3 - kswapd0 CPU up to 2.3 
> percent and no noticable slowdown of MIDI playback.
> 
> Mel Gorman's mm/compaction.c patch - kswapd0 CPU up to 20 percent and no 
> noticable slowdown of MIDI playback.
> 
> Thanks everyone for the help with this.

Ok then I think it's safer to go with compaction-no-kswapd-3.

I also created a git tree in case anybody else wants to test in easier
way.

git clone --reference linux-2.6.git git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git
(or "git clone git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git")
cd aa
git checkout -f 3d74399aaece29047beba13a81650538af8db67a
(compaction-kswapd+compaction_alloc_lowlat)
git checkout -f f048d0082bd3c6a1cc3f5e67aa5ef83d1561ec27
(compaction-no-kswapd+rest+compaction_alloc_lowlat)
git checkout -f 859e705548f7377b1803b05b2904bae77495fd1e (only
compaction_alloc_lowlat)

http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=shortlog;h=3d74399aaece29047beba13a81650538af8db67a
http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=shortlog;h=f048d0082bd3c6a1cc3f5e67aa5ef83d1561ec27
http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=shortlog;h=859e705548f7377b1803b05b2904bae77495fd1e

Arthur could you give one more spin to the
3d74399aaece29047beba13a81650538af8db67a tree? (or do you prefer an
updated patch compaction-kswapd-3?)

I'd like to get 3d74399aaece29047beba13a81650538af8db67a tested again
because I did one more modification included in the git version
compared to the patch version (nr_slab was not always initialized and
it could lead to slightly higher kswapd cpu load than intended). I
doubt it will help though (just in case).

Mel what you think? If f048d0082bd3c6a1cc3f5e67aa5ef83d1561ec27 is
still the only one that shows no regression, I think it's safe to
apply it to 2.6.38 and revert the compaction in kswapd feature. Then
we can add compaction to kswapd later with no hurry.

Thanks a lot for the help and quick feedback!
Andrea
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