[Bug 210780] Re: MTRRs set up incorrectly with 4GB RAM -> X slow

D. Hugh Redelmeier hugh at mimosa.com
Wed May 13 22:42:31 UTC 2009


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.

-- 
MTRRs set up incorrectly with 4GB RAM -> X slow
https://bugs.launchpad.net/bugs/210780
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