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:	Thu, 24 Feb 2011 08:25:43 +1030
From:	Arthur Marsh <arthur.marsh@...ernode.on.net>
To:	Andrea Arcangeli <aarcange@...hat.com>
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



Andrea Arcangeli wrote, on 24/02/11 07:55:
> 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.

One more combination I tried:

Mel Gorman's mm/compaction.c patch with Andrea Archangeli's 
kswapd-high_wmark + compaction-no-kswapd-3 patches - kswapd0 CPU less 
than 2 percent and no noticable slowdown of MIDI playback.

This may be better performing than compaction-no-kswapd-3 alone but is 
not conclusive.

>
> 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?)

If you can send me an updated patch compaction-no-kswapd-3 (I presume 
that kswapd-high_wmark is still needed) it would be easier for me to apply.

>
> 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
>

Arthur.
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