MythTV Front-End Performance Problems on Ubuntu

After upgrading to Ubuntu 8.10, I started having performance problems with video playback on MythFrontEnd.  I have a video encoder on my TV Tuner card, and I frequently record 2 show simultaneously, always with < 10% CPU utlization, so I knew mythbackend wasn't the problem.

The symptoms I saw were:

• Temporary “freezes” in video playback.  They lasted < 1/2 second each, and were spaced about 5-10 seconds apart at regular intervals.
• CPU running at 100%.  My CPU has been running at 30-50% busy during playback for the past 3 years or so, on the same hardware and OS.  So the 100% utilization is quite unusual.
• The freezes begin 5-10 minutes after playback begins
• running top shows high CPU usage in mythfrontend, but it also indicates other programs running with high CPU use, which is unusual. 

So I started an experiment:  each night I altered my MythTV settings and observing the running system. the next day  My family reported what they saw and I changed more settings.  I tried the following things:

• defragmenting the filesystem with xfs_fsr (I'm using XFS on LVM…perfect for mythTV's large files).
• inspecting cron jobs that run in the background
• removing unnecessary software
• changing my video driver and adjusting its settings (including compiz)
• restarting mythfrontend, mythbackend, and the computer
• killing running processes

It wasn't until I got to the last step–killing running processes–that I found a solution.  I kept seeing gnome-screensaver in the list of running processes, but it wasn't consuming a lot of CPU time.  But that's when it hit me….screensavers kick in after a period of keyboard and mouse inactivity, which could explain why the symptoms start several minutes after the beginning of a TV program.  And my efforts to catch the problem by suddenly bringing a process monitor into the foreground with <alt>-<tab> could be thwarted because of how screensavers react to keystrokes.  So I decided to kill the screensaver…

killall gnome-screensaver

and the problem went away. But it returned the next day. I found that the screensaver had been restarted. So I went into the screensaver settings in Gnome and deselected the “Screensaver” checkbox. That solved the problem too, and it didn't return.

Late in the problem solving process, I found a particular google search (this query) that revealed plenty of issues between MythTV and gnome-screensaver. Why is it that I find the answers after I solve the problem?