[coreboot] MTRR setup strategy

Eric W. Biederman ebiederm at xmission.com
Wed Jan 28 03:30:05 CET 2009

Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006 at gmx.net> writes:

> Assuming you don't have anything you want to cache near 4 GB (like flash):
> Both strategies are equally efficient if the contiguous cacheable area
> has a size of 2^n+2^(n-1).
> The additive strategy is more efficient if the size is 2^n+2^(n-k) and k>1.
> The subtractive strategy is more efficient if the size is 2^n-2^(n-k)
> and k>1.
> I hope that you accept this without a detailed mathematical proof. ;-)
>> I wonder... the subtractive strategy you subscribe is mentioned in
>> mtrr.c too and the comment claims it is implemented. But it very much
>> seems it is not.
> Ouch.

When did it break?

I remember the subtractive mtrr setup working correctly.
At least most of the time.


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