[mythtv-users] Jerky HD playback, only after resume from S3

[Leighton Brough]

I'm running 0.20-fixes as a combined BE/FE with a  2.6.18 kernel on a 
3.0GHz P4. If I start the system with a boot/reboot, then HD playback is 
perfect. However when I suspend to RAM (S3) and then resume, playback of 
some HD recordings (but not all) is jerky. I get messages like this in 
the log:

2006-10-10 12:21:32.194 WriteAudio: buffer underrun
2006-10-10 12:21:32.272 NVP: prebuffering pause
2006-10-10 12:21:32.272 WriteAudio: buffer underrun
2006-10-10 12:21:34.350 WriteAudio: buffer underrun
2006-10-10 12:21:34.510 WriteAudio: buffer underrun
2006-10-10 12:21:34.694 WriteAudio: buffer underrun
2006-10-10 12:21:36.676 WriteAudio: buffer underrun
2006-10-10 12:21:36.778 WriteAudio: buffer underrun

The jerky playback occurs even when there is no other significant 
activity on the box - no recording, commercial flagging, cronjobs etc. 
After a reboot, I would normally expect to be able to record 3 HD shows, 
run 3 commercial flagging jobs and watch a recording simultaneously 
without a hiccup, so there is plenty of CPU and disk performance 
available. Running top suggests that CPU usage for playback of the 
affected recordings is similar after a reboot and resume from S3. hdparm 
-t suggests that the disk performance is the same in both scenarios too.

I am at a loss as to what is different about the system before and after 
the suspend to RAM. Given the log messages above, where should I be 
looking to find the difference? I suspect some kernel module needs to be 
restarted, or some hardware state restored, but what?

I have real-time threads enabled, and am using ALSA for sound and the 
RTC for video timing, if that matters.

Thanks,
Leighton