[mythtv-users] Mythtv 0.24 Acer Revo ALSA WriteAudio buffer underruns

[Johnny Stenback]

On 02/10/2011 06:27 AM, pnetherwood at email.com wrote:
 >  > This is usually happening at the start of playback, while the
 > playeris buffering video ;
 >  > and then during playback if there is anythinghogging the CPU for a
 > short time.
 >
 > Interesting. I have my front end (Acer Revo) seperate to my backend
 > (Core i3) and it seems pause when the backend CPU goes to 100%. In all
 > cases its with mysqld when its running one of the scheduling queries.
 > Perhaps when the backend CPU is busy the frontends get momentarily
 > starved of data resulting in both audio and video buffer underruns. In
 > my last mail I was suggesting some query optimisation. I was wondering

Could be, but I'm seeing the same symptoms as you, w/o any correlation 
to CPU spikes on the backend. I repeated what you did, added logging for 
slow mysql queries, but there's no correlation here between the rare 
slow queries and the audio/video glitches I'm seeing (which didn't 
happen with 0.23 on the same hardware).

 From my testing this seems very unrelated to what happens on the 
backend, I can watch recordings on the backend w/o any noticeable change 
even when I introduce large IO disruptions (relative to streaming video 
to two frontends), or introducing CPU load on the backend (by doing a 
make -j4 of mythtv), or running two simultaneous commflagging jobs. So 
far, for me, these problems seem entirely unrelated to what happens on 
the backend.

 > if there was some temporary workaround; e.g increasing (or decreasing)
 > my ALSA or VDPAU buffers. Or maybe something with mysqld so that it
 > doesn't lock up the entire machine. With a my multi core CPU I'm amazed
 > it does go to 100%. Maybe there's some other bottleneck.

That seems strange, in my case the backend runs on a dual core core 2 
duo (2.93GHz), with the mysql db on a disk separate from recordings (on 
the same disk my os lives on), and I do occasionally see CPU spikes 
while streaming recordings. I wonder what the key difference is here?

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--
jst