xfree86 isn't setting mtrr registers
 

I'm running Xfree86 4.1.01. kernel 2.4.17 Debian 3.0r2 (woody). I built a kernel with mtrr support, and dmesg contains:

mtrr: v1.40 ...
mtrr: detected mtrr type: AMD K6

Also, /proc/mtrr exists.
X isn't, however, setting up the registers (/etc/proc is empty). On an earlier install of the same system (hardware, software) it worked fine, but I reinstalled, and now it doesn't. Any ideas?

I think I've solved my problem. My system has onboard video with an SiS chipset, and I'd been using the vesa driver in Xfree86. I had done so since the SiS driver didn't seem to be working properly, and the vesa worked fine. The SiS driver sets the mtrrs and screen performance is better (perhaps consequently; video performance certainly improves as a result, as I found once when I followed mplayer's suggestion and rebuilt the kernel to include mtrr support, not changing anything within X), but I had a hard time getting the screen res right and eliminating artifacts. I eventually apparently succeeded, though, after reading the SiS file within the X docs.