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SubjectRe: x86_64 ten times slower than i386
Andi Kleen wrote:
>> Jesse Barnes (cc:d) wrote a patch to address this, I think (x86: trim
>> memory not covered by WB MTRRs), but as far as I can tell it hasn't
>> been merged yet. System is Intel, 4gb of RAM.
>
> It wasn't merged because it broke booting on some systems.
> Besides the memory would be still lost -- all it did was to automate
> the "mem=XXXX" line.

There really are only two ways to deal with this -- drop the memory
(which should be automated, and a warning printed) or adjust the MTRRs.
The problem is that at some point we run out of MTRRs, partially
because they're masks instead of base/limit.

Even use of PAT doesn't trivially resolve this issue with less than
doing MTRR emulation via PAT (setting the default MTRR to WB); however,
that is bound to cause trouble with SMM.

-hpa
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