Re: 2.6.14-rt1 - xruns in a certain circumstance

["K.R. Foley" <kr@cybsft.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
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>

Mark,

If I am not mistaken, aren't you running the ivtv driver for your video
card (I think I have seen you on that list also)? Since that driver is
being developed outside the mainline kernel, isn't it likely that it
hasn't received many of the improvements that the rest of the kernel has
(latency and preemption wise)? Just a thought.
-- 

kr

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