Comment 36 for bug 210780

I'm now using Ubuntu 9.04 on my x61t.

GLXgears now reports varying amounts in the range 900 to 1150 without any mucking with MTRRs. That suggests that the Intel X video driver now uses the PAT mechanism. Good!

The MTRRs are still overlapping.

I had to change mtrr-uncover to deal with a gratuitous change made to the format of /proc/mtrr in kernel 2.6.28. You can get the newer version at ftp://ftp.cs.utoronto.ca/pub/hugh/mtrr-uncover-2009may13.tgz

Interestingly, fixing the MTRRs with mtrr-uncover and restarting X seemed to make glxgears run consistently at about 900. I have no idea why.

Adding "enable_mtrr_cleanup" flag to the appropriate "kernel" line(s) in your /boot/grub/menu.lst will also attempt to eliminate overlapping MTRRs. I don't know which Ubuntu kernel first included the cleanup code but it is in Jaunty's 2.6.28. On my system, the performance effect is the same as if you used mtrr-uncover. Of course it only operates at boot time.

There have been obscure cases where mtrr-uncover worked and enable_mtrr_cleanup did not.