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 12:10:45 +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 10:29:
> On Thu, Feb 24, 2011 at 08:25:43AM +1030, Arthur Marsh wrote:
>> 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.
>
> Applying Mel's patch on top should decrease latency more.
>
>> 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.
>
> It's a compaction-kswapd-3. It's likely going to work the same as the
> previous compaction-kswapd-2 (not as good as
> compaction-no-kswapd). It's better to apply both the kswapd-high_wmark
> and Mel's patch too (not only this one) during testing.

OK, with kswapd-high_wmark + compaction-kswapd-3 + Mel's patch (with the 
compaction initialisation fix), MIDI playback is fine.
kswapd0 CPU can very occasionally hit equal highest (17 percent was the 
highest I noticed, but is generally below the top 4-5 processes and less 
than 10 percent when working, dropping to around 0.3 percent when swap 
activity has subsided). This was with loading KDE 3.5.10, konversation, 
aptitude -u, icedove and iceweasel with several dozen tabs in addition 
to aplaymidi.

Regards,

Arthur.
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