Messages in this thread | | | Date | Mon, 05 Nov 2007 17:19:44 -0800 | From | "H. Peter Anvin" <> | Subject | Re: x86_64 ten times slower than i386 |
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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.
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