[mythtv] [PATCH] Realtime scheduling of video output thread

[John Patrick Poet]

Doug Larrick wrote:

> The attached patch implements POSIX realtime scheduling of the video 
> output thread.  This scheduling should allow smoother video output 
> under  higher loads / less heavyweight systems than is possible with 
> the current (default) scheduling.
>
> The patch implements a mechanism whereby mythfrontend (and also the 
> 'mythtv' program), if installed SUID root, first spawn a priveleged 
> thread and then drop priveleges to continue on as normal.  This 
> priveleged thread then hangs around to service requests to alter the 
> scheduling priority of other threads when requested; it is the only 
> part of MythTV that runs with elevated priveleges.
>
> When NuppelVideoPlayer starts up the video output thread, it then 
> requests realtime scheduling for it via this new mechanism.  If not 
> installed SUID root, this operation will fail (with a message) and 
> operation will proceed as it always has.
>
> The mechanism is flexible enough to allow performing other priveleged 
> operations in future if required.  For example, IIRC there's a video 
> decoder card (via?) that requires running as root.  Instead, this 
> priveleged thread could kick off the decoder thread only as root, 
> leaving the rest of MythTV running as a normal user.
>
> -Doug


Doug,

I have tried this.  Sure does not hurt.  I can't really tell if it helps.

I actually have a 3.2GHz HT P4 now, so the impact is probably small for me.

However, the work that you and Bruce have done lately has made a huge 
difference.  HD video plays nice and smooth -- even troublesome close-up 
pans.  Thank you both!

Lately I have noticed a non-reproducable hick-up every 5 to 10 minutes.  
It is just a quick micro-pause, and then it continues on fine.  If I 
rewind and play that part of the video again, it does not happen.  My 
impression is that the frontend is starved for data.  I need to check 
the log file to see if there are any clues there.

John