Re: MTRR fixup?

Rink Springer <rink_at_FreeBSD.org> writes:

> Hi Bernd,
>
> On Wed, Sep 03, 2008 at 05:49:44AM +0200, Bernd Walter wrote:
>> Some boards (including my Intel DG33BU) seem to have problems setting
>> up the mtrr to cache all RAM.
>> My system runs fast with 2G and ist about 6 times slower in buildworld
>> with 6G RAM.
>> I will try a BIOS update once Intels tells me why their update ISO
>> just turn the system off instead of updating the BIOS - sigh.
>> But it seems that Linux is doing some kind of fixup for MTRR:
>> http://lkml.org/lkml/2008/1/18/170
>> Can we do something similar?
>
> This is interesting, my motherboard (Intel DP965LT) seems to suffer from
> the same problem: putting 4GB of memory in it makes it dog slow, while
> putting 2GB in it makes it lightning fast...
>
> I've just given up trying to put 4GB of memory in this machine, but I
> believe this may help...

Yes, several Intel 965-based boards, including the DP965LT (which I have)
suffer from this problem.  See, e.g., 

http://article.gmane.org/gmane.os.freebsd.stable/50135/match=dp965lt

and the link therein.

> Please, keep me posted if the BIOS update fixes it for you.

I honestly haven't checked recently to see if there are recent BIOS upgrades
that fixed the problem; at the time I was messing with this last year, I found
that the BIOS upgrade their site claimed fixed the problem of "slowness in
machines with 4G or more RAM" did not in fact do so.  However, as someone
else on this thread pointed out, you can fix the bogus MTRR entry with
memcontrol, so I just stuck the appropriate script in /etc/rc.d to solve the
problem.