Messages in this thread | | | Date | Tue, 22 Feb 2011 08:37:23 +0100 | From | Clemens Ladisch <> | Subject | Re: [Alsa-user] new source of MIDI playback slow-down identified - 5a03b051ed87e72b959f32a86054e1142ac4cf55 thp: use compaction in kswapd for GFP_ATOMIC order > 0 |
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Arthur Marsh wrote: > I'm experiencing MIDI playback slow-downs when I'm observing kswapd0 > active (a few percent of cpu in top output) in recent kernels. > > I git-bisected the problem down to: > > commit 5a03b051ed87e72b959f32a86054e1142ac4cf55 > Author: Andrea Arcangeli <aarcange@redhat.com> > Date: Thu Jan 13 15:47:11 2011 -0800 > > thp: use compaction in kswapd for GFP_ATOMIC order > 0 > > This takes advantage of memory compaction to properly generate pages of > order > 0 if regular page reclaim fails and priority level becomes more > severe and we don't reach the proper watermarks. > > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> > > I ran git-bisect over the weekend, building and installing ALSA 1.0.24 > with each kernel. After identifying the above commit, I rebuilt the 2.6 > head with that commit reverted and verified that the problem was no > longer present.
Apparently, huge page compaction disables interrupts for much too long.
> MIDI playback was via aplaymidi -p 17:0 to a Soundblaster Audigy 2 ZS > (SB0350) wavetable.
The ALSA sequencer uses either the system timer or an HR timer at 1 kHz to deliver MIDI commands (notes); the wavetable driver requires its own interrupts in regular 5.3 ms intervals.
Regards, Clemens
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