Re: [gentoo-user] dmesg warning about mtrr: type mismatch and allocation failed

[Paul Hartman <paul.hartman+gentoo@gmail.com>]

On Sun, Aug 15, 2010 at 6:27 PM, Walter Dnes <waltdnes@waltdnes.org> wrote:
>  I'm running 64-bit Gentoo on an Intel 4-core i3 with an Intel integrated
> graphics controller.  An excerpt from dmesg follows, with the video-
> related stuff.  Note the two lines that I've split off.  They mention
> the mtrr type mismatch and the allocation failure.  Is this a problem
> and if so, what do I do about it?

...

> [    0.608643] mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining
> [    0.608725] [drm] MTRR allocation failed.  Graphics performance may suffer.

I had a similar message, it was there because of the fact that i
specified the wrong (or failed to specify?) mtrr method in my kernel
boot parameters for the framebuffer. I'm using uvesafb and in kernel
documentation (/usr/src/linux/Documentation/fb/uvesafb.txt) it
explains the values and even gives an example of this error and what
to do about it:

<cut>
mtrr:n  Setup memory type range registers for the framebuffer
        where n:
              0 - disabled (equivalent to nomtrr) (default)
              1 - uncachable
              2 - write-back
              3 - write-combining
              4 - write-through

        If you see the following in dmesg, choose the type that matches
        the old one.  In this example, use "mtrr:2".
...
mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
...
</cut>

After I changed my mtrr setting in grub's config & rebooted, the error
message went away.

HTH :)