[mythtv-users] Realtime - Kernel Scheduler - Preemption

Steve Malenfant smalenfant at gmail.com
Sat Apr 8 17:39:26 UTC 2006


I think I have an answer for question 1).  top will show you only the
main thread.  If you want to verify that it's working properly, use ps
-eLlf (or something like it).  You should see different priorities for
different thread of the mythfrontend.  I verified that and it works
for me when I use root to lauch mythfrontend and enabled real-time
priority.

Hoperfully what I'm saying is accurate.

For example, I see that my mythbackend has 13 threads...  Some are
using different priorities (from 75-78)

Steve M.

On 4/7/06, Steve Skarda <steveskarda at gmail.com> wrote:
> I have been trying to fix problems with a 100-200mS delay in audio and that
> has created a lot of questions around how the Linux Schedule works and
> whether or not MythTV is getting the CPU it needs or not.  Here are
> questions that I am hoping someone can help shed light on.
>
> 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?
>
> 2).  Any idea how to up the task priority on mythfrontend for the Linux
> scheduler?
>
> 2).  I tried compiling a new kernel with preemptive scheduling turned on (my
> old kernel was set to voluntary/desktop).   I also tried to update PAM to a
> newer version.  I am not sure what went wrong but Mythfrontend CPU went near
> 100%.  This is very unusual for my 3.2Ghz Pentium.   Older posts seem to
> suggest that the problem is that mythfrontend can't get the CPU as often as
> it needs.  I tried rtlimits, pam, realtime-lsm.  Nothing seemed to help.  I
> always see "using realtime" in the logs but CPU is high causing prebuffering
> pauses.  Not sure if the problem is with my new kernel or something I messed
> up in the PAM.
>
> 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.
>
> My system for anyone that is curious:
> Ubuntu Breezy
> Vanilla 2.6.15 kernel
> Pentium 4 3.2Ghz w/HT
> Nothing unusual in the logs
> MythTv from SVN
>
> Steve
>
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