poll: problems with MTRRs?

[Lennart Sorensen]

On Sun, Mar 15, 2009 at 04:58:18PM -0400, D. Hugh Redelmeier wrote:
> How many of you have x86 computers with 4G or more of RAM?

I have 6GB in my mythtv box (which did cause some initial issues that
I worked around using some not so normal methods).

> On many such systems, the MTRRs are set up by the BIOS in a way that
> conflicts with X.

Mine works fine.  I have only ever heard of intel boards and a few
gigabyte boards gettings this wrong.  Of course since I only personally
use asus boards and they never appear to have had the mtrr bugs, I can't
say much there.

> I have this problem in both of my machines with 4G or more of RAM (IBM
> ThinkPad x61t and HP Pavilion A6245n).
> 
> Could you run the following command and tell me about your system if
> if grep prints anything?
> 	dmesg | grep -i mtrr
> 
> You might see things like:
>   mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining
>   mtrr: no MTRR for d0000000,10000000 found

In fact none of the kernels I have looked at have mtrr stuff printed in
dmesg anymore.  I think they stopped doing that a few years ago.  How old
is your kernel?

> I'd like to know what distro you are running (/etc/issue) and
> what kernel you are running (/proc/version).
> 
> I'd like to know what your MTRR's look like.  Could you tell me what
> /proc/mtrr says?
> 
> I hope to be able to help you if you do find these messages in the
> dmesg output.

Well certainly newer kernels have tried to deal with some of these bugs,
although apparently the real solution is for X to start using PAT rather
than MTRR since the 8 entry MTRR is awfully limited given todays ram
quantities.

Well here is the /proc/mtrr of one box with 8GB ram running Debian Etch
at the moment with the 2.6.24 etchnhalf kernel (amd64 of course):

reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0x100000000 (4096MB), size=4096MB: write-back, count=1
reg03: base=0x200000000 (8192MB), size=8192MB: write-back, count=1
reg04: base=0x400000000 (16384MB), size=16384MB: write-back, count=1
reg05: base=0x800000000 (32768MB), size=32768MB: write-back, count=1
reg06: base=0xd0000000 (3328MB), size=  16MB: write-combining, count=1

Strangely it doesn't appear in dmesg.  No idea why.  It only has 8GB ram,
but seems to have setup a much larger mtrr range.  X works fine though.
System is an IBM X3650.

Here is my mythtv box with 6GB ram on an Asus P5K board (using a P5K-R
bios to get AHCI mode on the ICH9 SATA controller which allows 64bit
dma rather than the 32bit dma limit in IDE mode):

reg00: base=0xd0000000 (3328MB), size= 256MB: uncachable, count=1
reg01: base=0xe0000000 (3584MB), size= 512MB: uncachable, count=1
reg02: base=0x00000000 (   0MB), size=4096MB: write-back, count=1
reg03: base=0x100000000 (4096MB), size=2048MB: write-back, count=1
reg04: base=0x180000000 (6144MB), size= 512MB: write-back, count=1
reg05: base=0x1a0000000 (6656MB), size= 256MB: write-back, count=1

No problem there either.  Running 2.6.26 amd64 kernel with Debian
unstable.

-- 
Len Sorensen
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