When I went to upgrade my server to the 2.6.9 kernel (which it turns out I can’t use at the moment anyway for other reasons), I discovered that I still had some debugging options enabled in my current kernel config, from a problem I had over a year ago. OOPS.
I wouldn’t have expected it to make *that* much of a difference, but after recompiling 2.6.7 without them set I can now play back recordings in MythTV at full speed, using around 80% CPU. It still stutters slightly whenever something else kicks in, like a web server hit, but it’s still a vast improvement.
Now I just have to solve the frigging B&W video problem. Hopefully a new-but-cheap GeForce 4 that’s on the way will fix that…