[alsa-devel] /dev/snd/timer behavior
Ron Cococcia
ron.cococcia at request.com
Thu Apr 16 23:54:51 CEST 2009
Hello,
We have been attempting to debug an issue that we have been having for a
few weeks related to audio playback. Specifically, over time, the
playback of audio gets 'stuck' for a while (60 seconds or so), then
quickly advances forward again (for about 60 seconds), then gets stuck
again. It continues to repeat this until I either stop playback or
pause/play. We have dubbed it 'skip-lock' as it skips ahead, then locks
for a bit. It takes a while to reproduce this behavior, typically
around 6 hours.
We have about 30 of these systems setup, each with the same hardware
configuration. They have a VIA C7 CPU (1.5GHz), 1GB RAM, and they are
using the VIA 8233A AC97 controller with an ALC655 codec. The system is
SATA based (using sata_via), and an RTL8110 gigabit ethernet controller
(using rtl8169).
For the OS, we are using Debian Etch with the 2.6.29 kernel, and we have
tested a number of these units with 2.6.24-etchnhalf as well. ALSA lib
1.0.13 (from the install) is still in use, but I am trying out 1.0.19 on
a few of the units to see if it helps. The player we use is called
BlueTune, which we have used in older systems for years without
trouble. I plan on trying to set up another player app to do the same
testing, but haven't had the time to do that yet. On most of the
systems, the player is using the default alsa output. I have configured
a few systems to use plughw:0,0,0 for playback (mainly so that
/dev/snd/timer is not used), and they have not had any playback issues
so far (about 24 hours so far).
After a bunch of other tests, we started to run strace against the
player. We saw that it was repeatedly getting EAGAIN when reading from
/dev/snd/timer during the 'stuck' phase. I have started to poke around
a bit more in the timer code and see why EAGAIN is repeatedly being
generated (in snd_timer_user_read, tu->qused is stuck at 0 for a
while). I figured that if anybody had some things to try or places to
look, it might save a bit of time in finding the cause of this issue.
Thanks!
Ron
PS: I apologize if this is the wrong place to post this. I had posted
a not-terribly-detailed message to alsa-user a few weeks ago, but have
gained more data that I felt fit better here.
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