MTRR survey: better X performance on systems with 3G or more RAM

[D. Hugh Redelmeier]

| From: D. Hugh Redelmeier <hugh at mimosa.com>

| | From: Bob Marcan <bob.marcan at gmail.com>

| I'm quite surprised at your observations.

| (The other thing I noticed is that your glxgears performance is very
| very good.  This may indicate that something else is going on.
| Perhaps the intel driver now uses PAT.  I'm going to ignore this
| possibility for now.)

I now think that recent open-source intel drivers use PAT.  I don't
have a suitable test box with Fedora but I've got one running Ununtu
8.10 and Ubuntu 9.04 beta.  This is my ThinkPad x61t with 4GiB of RAM.

- the video buffer's address range has an MTRR that is covered by
  another

- under 8.10, performance is increased if the MTRRs are rearranged

- under 9.04 beta performance is good even with the default MTRR
  setup.

This matches Bob Marcan's observation with Fedora 10 on his box.

Thanks, Bob, for your help.