Thread Priority

[MrD]

Is this option required on Linux?

-XX:ThreadPriorityPolicy=1

It's not there on SageTV 6 and it requires root to be enabled.

According to Sun:

A thread priority regression in J2SE 5.0 has been corrected in Java SE 6 as well as J2SE 5.0, Update 6. Correct behavior is restored and a workaround no longer is needed.

On Windows, by default Java thread priority MAX_PRIORITY is no longer mapped to the highest native priority (THREAD_PRIORITY_TIME_CRITICAL). Instead it is mapped to THREAD_PRIORITY_HIGHEST. This change is necessary because THREAD_PRIORITY_TIME_CRITICAL threads may interfere with system threads and affect system responsiveness.

If you need to revert to the prior behavior (THREAD_PRIORITY_TIME_CRITICAL), you can set -XX:ThreadPriorityPolicy=1 .

[Narflex]

It's not required...but you get better performance with it on since thread priorities will then be obeyed instead of making every thread the same priority.

[drewg]

Originally Posted by Narflex

It's not required...but you get better performance with it on since thread priorities will then be obeyed instead of making every thread the same priority.

Would a viable alternative be to use -XX:ThreadPriorityPolicy=9999 to avoid the root requirement? Apparently, this will cause java threads to run at different priorities, where the highest priority java threads have "normal" priority, and the lowest have "nice" (low) priority. This means that low priority java threads might be starved on a CPU bound host running another (non-sage) job (like ffmpeg transcoding).

See http://tech.stolsvik.com/2010/01/lin...orkaround.html for a detailed description of this.

Speaking of priorities, is it possible to have sagetv start ffmpeg niced when doing transcodes? At least in V6, ffmpeg runs at "normal" priority when transcoding.

Drew

[MrD]

Originally Posted by drewg

Would a viable alternative be to use -XX:ThreadPriorityPolicy=9999 to avoid the root requirement?

This depends on a bug in the Java implementation -- which means it would work until the bug it fixed.

[drewg]

Originally Posted by MrD

This depends on a bug in the Java implementation -- which means it would work until the bug it fixed.

As long as you don't updated the JVM, you're fine. The thing I'm really concerned about is that sage's "normal" priority threads would really be niced, and would get swamped by things like ffmpeg transcode jobs.

Drew

[Narflex]

Originally Posted by drewg

Speaking of priorities, is it possible to have sagetv start ffmpeg niced when doing transcodes? At least in V6, ffmpeg runs at "normal" priority when transcoding.

Drew

I was going to post that it already did that....but then decided to look at the code first. Apparently we hadn't added 'nice' when doing transcoding (it does use nice for all other ffmpeg usage already)...but now it's been added for the next build.

And on Windows it was already reducing the process priority...not that you'd care about that though.