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



| From: Bob Marcan <bob marcan gmail com>

Thanks very much for trying this.

I'm quite surprised at your observations.

It looks to me as if your video card's buffer needed to be uncovered
but the performance you observed didn't improve significantly.  I've
never seen that before.

I'm wondering if my instructions were not clear enough and as a result
you ran the "after" test without the benefit of uncovering.

(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.)

mtrr-uncover without flags tells you what it would do.  You need to
run it as root with the --execute flag for it to actually do the MTRR
adjustment.
	# /home/bob/tmp/01/mtrr-uncover/mtrr-uncover --execute

The second thing that could imagine going wrong is that you might have
rebooted after running mtrr-uncover --execute, before running
glxgears.  Rebooting wipes out any changes made by mtrr-uncover.

Could you run mtrrr-uncover, with no flags, just before running
glxgears?  If the MTRRs have been adjusted correctly, mtrr-uncover's
last output line should say:
	No changes made.

In summary, here's what I'd like you to try:

	as superuser, fix MTRRs:
		 /home/bob/tmp/01/mtrr-uncover/mtrr-uncover --execute
	restart X:
		CTRL-ALT-Backspace
	check that the MTRR changes stuck (expect "No changes made"):
		/home/bob/tmp/01/mtrr-uncover/mtrr-uncover
	check that X set write-combining (expect one line of output):
		grep write-combining /proc/mtrr
	check performance:
		glxgears

Could you send me a copy of your /var/log/Xorg.0.log after this test?
I don't think that there would be anything confidential in it.


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