[mythtv-users] Realtime - Kernel Scheduler - Preemption

Steve Skarda steveskarda at gmail.com
Mon Apr 10 15:31:24 UTC 2006


On 4/8/06, Tony Lill <ajlill at ajlc.waterloo.on.ca> wrote:
>
>
> > 1).   I have realtime enabled in Ubuntu.   When I launch a recording,
> "using
> > realtime prioirty" shows up in the log.   When I look at TOP, under the
> PR
> > column, I see that Mythfrontend priority is similar to other programs,
> > around the 30's.  However, there are a few tasks, with 'RT" as priority,
> > presumably reatltime.   Should I expect to see RT for mythfrontend task
> as
> > well?
>
> That depends. Does ps show one "process" or many for mythfrontend? The
> frontend runs multiple threads, but only puts one of them in realtime
> mode for playback. The latest ps on Debian hides the threads. Try
> intalling htop, that will show them.


That helps.  I ran htop, and I see a threads with a priority of -2.  Assume
that means realtime.  Makes sense now.  Thank you!


> 3).  I have gotten no where near solving my audio sync issues.  I have
> been
> > considering compiling a kernel with Ingo's realtime patch.  There have
> been
> > two posts on that subject.  One saying that MythTv works and another
> asking
> > if it is possible.   Does anyone have further information on this?  So
> far,
> > I have had trouble getting it to compile and I am expecting to have
> > difficulty getting NVidia to work.
>
> I have a suspicion that all the changes that have been put into the
> 2.6 kernels to make it work really well for enterprise servers or
> desktop have boned it for multimedia. Have you tried running a 2.4
> kernel? All my recording problems started when I went from 2.4 to
> 2.6. If I wasn't so damned stubborn....


I have built my system on Ubuntu and they are talking about including a
real-time kernel in the post Dapper version.   Looking forward to that.  If
I get ambitious, I might take another crack at compiling a vanilla kernel
with real-time patches.  I haven't been able to do that successfully yet,
but I am sure it is possible.

Also are you sure the audio sync problems are in the playback,
> and not the recording?


I have no idea where the problem is to be honest.   It is pretty consistent
that I will see 200mS delay in audio on HDTV programs (more so on 1080i,
that 720p).    I have posted  that issue  before but didn't get any replies
which caused me to assume either I am too sensitive or others don't have the
same problem.  Got any ideas on how to troubleshoot a recording issue?  I am
using Fusion 5 Gold cards which are not very popular so it wouldn't surprise
me if that was the problem.

Off Topic, but funny-
My tardy reply was due to the fact that in my attempts to ensure I had
realtime priority, I installed a new version of Pam over the Ubuntu's old
version.  Well, folks that understand PAM better than me probably know
better than do that.  Long story short, I bonked my whole system so I spent
a day rebuilding it.   For anyone that has "been there, done that" to top it
all off, I decided to be smart and make detailed journal of the steps to get
it working.  Didn't realize that OpenOffice used the tmp directory (since I
started the document from an email attachment) and I lost all of my great
documentation after a reboot.  Oh, well.  By the way, even with my new
system on Ubuntu Dapper and newer version of PAM, I still have audio delay.
grumble.
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