View Full Version : [ubuntu] mtrr in Karmic?

November 7th, 2009, 08:11 PM
Is it necessary to set up mtrr in Karmic like it was in Jaunty?

I have a nVidia 6200, and I setup mtrr in Jaunty by putting this line into

echo "base=0xe0000000 size=0x10000000 type=write-combining" >| /proc/mtrr
(The actual text to use inside the quotes depends on your particular graphics card).

One can check if the desired result was obtained by typing in a terminal

cat /proc/mtrr

However, in Karmic, with my /etc/gdm/PostLogin/Default edited to set up mtrr, it looks like either /etc/gdm/PostLogin/Default is not executed, or the echo line added is ignored, as the mtrr settings do not change.

However if I enter the command directly in the terminal:

sudo -s
echo "base=0xe0000000 size=0x10000000 type=write-combining" >| /proc/mtrr
then the changes take effect (but they get lost after a reboot, hence the reason for editing /etc/gdm/PostLogin/Default, but that trick no longer works in Karmic).

Do I need to set mtrr in Karmic?
If so, how?

November 7th, 2009, 11:31 PM
Maybe I misunderstand - was mtrr just a fix for Intel GPUs?
Even so, why is Karmic ignoring the edit to /etc/gdm/PostLogin/Default, when Jaunty executed it fine?

November 8th, 2009, 06:01 PM
Sunday bump.

November 9th, 2009, 11:44 PM
From http://blog.nachtarbeiter.net/tag/mtrr/

The bug is a miscommunication between X.org and the Kernel, which results in a misconfiguration of the Memory Type Range Registers (MTRR) in the Kernel. The result is poor performance in video playback and everything that involves graphics in general. This bug has been fixed upstream and in Karmic. A fix for Jaunty has been developed, but is yet to be released.

You can test, if you are affected, by running cat /proc/mtrr on the command line. If you canít see a line, which ends in write-combining you are most certainly affected by this. You can further check with lspci -vv and check the Region 0 memory range of your VGA adaptor. If you cant find that memory range in your mtrr file, you are probably affected.

So is the bug fixed in karmic?

November 11th, 2009, 10:23 PM
Maybe I misunderstand - was mtrr just a fix for Intel GPUs?

I think mtrr relates to Intel CPUs.

Can anyone offer any more info?

November 15th, 2009, 04:40 PM
Another xSundayx Tuesday bump.

November 22nd, 2009, 10:47 PM
Sunday bump

November 29th, 2009, 04:28 PM
Sunday bump for any clues

December 4th, 2009, 11:27 PM
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/446480 says PAT will be enabled in karmic.

My /boot/config-2.6.31-15-generic contains


So does this mean I don't need to set up mtrr ?

December 12th, 2009, 05:39 PM
Saturday bump

December 24th, 2009, 06:52 PM
Well I found that setting the mtrr up inside /etc/rc.local works in Karmic. Putting it in /etc/gdm/PostLogin/Default results in it being ignored.

I got a very slight increase in performance, using the test site

Nothing to write home about, though : 8.2Hz went to 9Hz.

So mtrr seems to make some difference. But is it really needed under Karmic?

January 3rd, 2010, 08:47 PM