about mtrr

about mtrr

[Volker Armin Hemmann]

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Hello,
this is an amd64 system. AMD X2 CPU, Am2+ motherboard with A770 chipset and SB 
700 southbridge -A770Crossfire from Asrock. Latest bios

my /proc/mtrr always roughly looking like that:
reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
reg02: base=0x0c0000000 ( 3072MB), size=  128MB, count=1: write-back
reg03: base=0x0c8000000 ( 3200MB), size=   64MB, count=1: write-back
reg04: base=0x0cc000000 ( 3264MB), size=   32MB, count=1: write-back
reg05: base=0x0ce000000 ( 3296MB), size=   16MB, count=1: write-back

now it looks like that (with ati driver loaded, without, just the last line is 
missing):

cat /proc/mtrr
reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
reg02: base=0x0c0000000 ( 3072MB), size=  128MB, count=1: write-back
reg03: base=0x0c8000000 ( 3200MB), size=   64MB, count=1: write-back
reg04: base=0x0cc000000 ( 3264MB), size=   32MB, count=1: write-back
reg05: base=0x0ce000000 ( 3296MB), size=   16MB, count=1: write-back
reg06: base=0x0d0000000 ( 3328MB), size=  256MB, count=1: write-combining

which was ok as long as I had 4gb of ram.

But I have a 6gb now - and with the additional 2gb performance took a hit.

I would like to know why roughly 2.5gb are not covered by mtrr's and is there 
a way to force the kernel to cover the whole range without doing it manually?
I played with mtrr_spare_reg_nr= and MTRR cleanup support  without any changes 
at all. 
2.6.27, 2.6.28, 2.6.29 - all three versions show the same mtrr.
Attached are dmesg and config.

Glück Auf,
Volker

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