https://bugzilla.novell.com/show_bug.cgi?id=775694 https://bugzilla.novell.com/show_bug.cgi?id=775694#c5 --- Comment #5 from Mel Gorman <mgorman@suse.com> 2012-08-16 09:50:05 UTC --- (In reply to comment #4)
OK, then it gets more interesting and my patch isn't going to help. So the music is on a separate, otherwise unused disk.
And the information on the USB disk being read so it's not like we're waiting on data to be written to slow storage. Is there any possibility that a barrier due to the write on ext4 can cause a read on a ext3 USB stick to be delayed? Hubert, what are the mount options used for the USB stick? In particular, is it mounted with atime because that would mean that a write is necessary when accessing a file which could be delayed for a long time.
That means that the problem shouldn't be caused by disk being busy due to other IO. The only idea I have is that reclaim is too eager and reclaims some of the loaded music data / player executable (due to dirty pages from large copy putting stress to reclaim).
That seems unlikely, the amount of data needed by the music player should be so low that I find it hard to believe it's getting reclaimed that quickly. That said the most recent round of backports for the 3.1 kernel included a fix for keeping mapped file pages resident but I don't think it'll fix this particular problem but if you build a test kernel with your ext3 latency fixes then it'll also include those reclaim fixes.
But to confirm this we'd need some back traces of blocked processes when audio stalls happen I guess. Mel, do you have other ideas?
If Huburt could capture vmstat -n 1 during the whole test it would be useful to see if swapping is actually happening. Second, capturing a log of the following substituting MUSICPLAYER for whatever the music player process is called should tell us where it is stalling while [ 1 ]; do date; cat /proc/`pidof MUSICPLAYER`/stack; sleep 1; done We also know from https://lkml.org/lkml/2012/7/10/132 that read latencies for ext3 can be very bad. Hubert, to see if this is ext3 specific would it be possible for you to test with a similarly sized USB stick formatted with ext4 instead of ext3 please? -- Configure bugmail: https://bugzilla.novell.com/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.