2.6.14-rt1 - xruns in a certain circumstance

[Mark Knecht <markknecht@gmail.com>]

Hi,
   I've been running 2.6.14-rt1 today. For the most part there seem to
be no changes for me from 2.6.14-rc5-rt3. One place I saw xruns
earlier is still there and I do not understand why this situation
should be able to create xruns.

   I really think there is something to be learned from this problem.
The way I see it What's going on with Myth is completely separate from
what's going on with Jack, but Myth is causing xruns somehow.

1) I have Jack running. It is using sound card #2, my RME HDSP 9652. I
can run for hours and see no xruns.

2) I start MythTV using sound card #1. Within MythTV there are
essentially 3 types  of operation:

a) Basic menus
b) Preview menu
c) Full screen video watching

What I'm seeing is that when using basic menus, or when watching
videos I get no xruns. However, if I'm in the preview menu I get an
xrun every few minutes. In the following snippet I started Jack and
ran for about 20 minutes with no problems. I was using MythTV and
watching videos. I spent very little time in the preview menu:

16:19:26.184 Server configuration saved to "/home/mark/.jackdrc".
16:19:26.185 Statistics reset.
16:19:26.411 Client activated.
16:19:26.412 Audio connection change.
16:19:26.415 Audio connection graph change.
16:20:34.918 Audio connection graph change.
16:20:34.977 Audio connection change.
16:20:37.842 Audio connection graph change.

At about 4:45PM I exited the videos and left Myth sitting in a preview
menu. In this mode Myth puts a small video screen in the bottom right
corner where oyu get a low quality picture so you can see what the
start of the program looks like. While sitting in this mode for about
45  minutes I got 10 xruns:

16:45:45.670 XRUN callback (1).
**** alsa_pcm: xrun of at least 0.663 msecs
16:47:41.697 XRUN callback (2).
**** alsa_pcm: xrun of at least 0.415 msecs
subgraph starting at qjackctl-8363 timed out (subgraph_wait_fd=17,
status = 0, state = Finished)
17:06:47.023 XRUN callback (3).
**** alsa_pcm: xrun of at least 0.781 msecs
**** alsa_pcm: xrun of at least 4.924 msecs
17:06:49.003 XRUN callback (1 skipped).
subgraph starting at qjackctl-8363 timed out (subgraph_wait_fd=17,
status = 0, state = Finished)
17:15:36.697 XRUN callback (5).
**** alsa_pcm: xrun of at least 0.831 msecs
**** alsa_pcm: xrun of at least 2.850 msecs
17:15:37.707 XRUN callback (1 skipped).
17:17:38.387 XRUN callback (7).
**** alsa_pcm: xrun of at least 0.617 msecs
subgraph starting at qjackctl-8363 timed out (subgraph_wait_fd=17,
status = 0, state = Finished)
17:18:52.275 XRUN callback (8).
**** alsa_pcm: xrun of at least 1.654 msecs
17:20:44.214 XRUN callback (9).
**** alsa_pcm: xrun of at least 0.664 msecs
17:28:00.610 XRUN callback (10).
**** alsa_pcm: xrun of at least 0.244 msecs
subgraph starting at qjackctl-8363 timed out (subgraph_wait_fd=17,
status = 0, state = Finished)

At this point I exited the preview menu and went to a higher level
menu and just let the machine sit in Myth for about 20 minutes. No
xruns: At about 5:50PM I went back into the preview menu and got an
xrun within 2 minutes:

17:51:59.548 XRUN callback (11).
**** alsa_pcm: xrun of at least 1.156 msecs
17:52:32.464 XRUN callback (12).
subgraph starting at qjackctl-8363 timed out (subgraph_wait_fd=17,
status = 0, state = Finished)
**** alsa_pcm: xrun of at least 1.326 msecs

   Note that on this machine I can browse the web, transfer files via
the network, build kernels, do an emerge world, run cpuburn, etc., and
I get no xruns. However, if I run MythTV in the preview menu I get
them consistently.

   Also note that the MythTV server is actually located over a
wireless connection. There is no wireless on my machine - the
connection is between the router and the machines in another part of
the house. I bring this up in case it indirectly bears upon the
networking, etc.

   I look forward to hearing what you all think I should look at here.

   I have not yet turned on the preempt debugging stuff. I'll work on
that after I hear back that I'm not wasting my time.

Thanks,
Mark