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MTRR mystery (Announce)

posted by roytam, 31.01.2012, 05:38

> > When I come at home I'll try pull one DIMM out.
>
> Yes, I was right! I pulled 1 DIMM out and got back my VESA hyper speed. But
> why? I did some comparison. First here's output of Japhet's memstat.
> for 2GB:
>
> Int 15h, ah=88h, extended memory: 0 kB
> Int 15h, ax=E801h:
> ext. memory below 16 MB: 15360 (0x3c00) KB
> ext. memory above 16 MB: 32494 64 KB blocks = 2030 MB [1000000-7fedffff]
> Int 15h, eax=E820h:
> addr 000000000, size 00009f800, type 1 (available)
> addr 0000f0000, size 000010000, type 2 (reserved)
> addr 0fec00000, size 001400000, type 2 (reserved)
> addr 0f0000000, size 004000000, type 2 (reserved)
> addr 00009f800, size 000000800, type 2 (reserved)
> addr 07fef0000, size 000010000, type 2 (reserved)
> addr 000100000, size 07fde0000, type 1 (available)
> addr 07fee3000, size 00000d000, type 3 (ACPI)
>
> for 4GB:
>
> Int 15h, ah=88h, extended memory: 0 kB
> Int 15h, ax=E801h:
> ext. memory below 16 MB: 15360 (0x3c00) KB
> ext. memory above 16 MB: 57070 64 KB blocks = 3566 MB [1000000-dfedffff]
> Int 15h, eax=E820h:
> addr 000000000, size 00009f800, type 1 (available)
> addr 0000f0000, size 000010000, type 2 (reserved)
> addr 0fec00000, size 001400000, type 2 (reserved)
> addr 0f0000000, size 004000000, type 2 (reserved)
> addr 00009f800, size 000000800, type 2 (reserved)
> addr 0dfef0000, size 000010000, type 2 (reserved)
> addr 000100000, size 0dfde0000, type 1 (available)
> addr 0dfee3000, size 00000d000, type 3 (ACPI)
> addr 0dfee0000, size 000003000, type 4 (ACPI)
>
> Then I checked how MTRRs are set with 2GB.
> before:
>
> VESA 3.0 NVIDIA [262144 kB]
> LFB address: E0000000h
> MTRR #0 = 000000000, 06; 080000000, 1
> MTRR #1 = 07FF00000, 00; 0FFF00000, 1
> MTRR #2 = 000000000, 00; 000000000, 0
> MTRR #3 = 000000000, 00; 000000000, 0
> MTRR #4 = 000000000, 00; 000000000, 0
> MTRR #5 = 000000000, 00; 000000000, 0
> MTRR #6 = 000000000, 00; 000000000, 0
> MTRR #7 = 000000000, 00; 000000000, 0
> MTRR area E0000000-EFFFFFFFh was set to mode: WC
>
> after:
>
> VESA 3.0 NVIDIA [262144 kB]
> LFB address: E0000000h
> MTRR #0 = 000000000, 06; 080000000, 1
> MTRR #1 = 07FF00000, 00; 0FFF00000, 1
> MTRR #2 = 0E0000000, 01; 0F0000000, 1
> MTRR area E0000000-EFFFFFFFh was set to mode: WC
>
> And now with 4GB.
> before:
>
> VESA 3.0 NVIDIA [262144 kB]
> LFB address: E0000000h
> MTRR #0 = 000000000, 06; 000000000, used
> MTRR #1 = 0E0000000, 00; 0E0000000, used
> MTRR #2 = 000000000, 06; 0E0000000, used
> MTRR #3 = 0DFF00000, 00; 0FFF00000, used
> MTRR #4 = 000000000, 00; 000000000, unused
> MTRR #5 = 000000000, 00; 000000000, unused
> MTRR #6 = 000000000, 00; 000000000, unused
> MTRR #7 = 000000000, 00; 000000000, unused
> MTRR area E0000000-EFFFFFFFh was set to mode: WC
>
> after:
>
> VESA 3.0 NVIDIA [262144 kB]
> LFB address: E0000000h
> MTRR #0 = 000000000, 06; 000000000, used
> MTRR #1 = 0E0000000, 01; 0F0000000, used
> MTRR #2 = 000000000, 06; 0E0000000, used
> MTRR #3 = 0DFF00000, 00; 0FFF00000, used
> MTRR #4 = 000000000, 00; 000000000, unused
> MTRR #5 = 000000000, 00; 000000000, unused
> MTRR #6 = 000000000, 00; 000000000, unused
> MTRR #7 = 000000000, 00; 000000000, unused
> MTRR area E0000000-EFFFFFFFh was set to mode: WC
>
> I also tested Windows NT 4.0 with VBEMP driver and they was not affected
> (run fast as usual). So I dumped MTRRs with my CPUID utility and hardcoded
> to MTRRLFBE:
>
> This is how WinNT 4.0 + VBEMP set MTRRs:
>
> MTRR RAW values
> MSR [00000200h] = 0000000000000006h MSR [00000201h] = 0000000F80000800h
> MSR [00000202h] = 0000000080000006h MSR [00000203h] = 0000000FC0000800h
> MSR [00000204h] = 00000000C0000006h MSR [00000205h] = 0000000FE0000800h
> MSR [00000206h] = 00000000DFF00000h MSR [00000207h] = 0000000FFFF00800h
> MSR [00000208h] = 00000000E0000001h MSR [00000209h] = 0000000FF0000800h
> MSR [0000020Ah] = 00000000F0000006h MSR [0000020Bh] = 0000000FF0000800h
> MSR [0000020Ch] = 0000000100000006h MSR [0000020Dh] = 0000000FE0000800h
> MSR [0000020Eh] = 0000000000000000h MSR [0000020Fh] = 0000000000000000h
>
> MTRR parsed values
> VESA 3.0 NVIDIA [262144 kB]
> LFB address: E0000000h
> MTRR #0 = 000000000, 06; 080000000, used
> MTRR #1 = 080000000, 06; 0C0000000, used
> MTRR #2 = 0C0000000, 06; 0E0000000, used
> MTRR #3 = 0DFF00000, 00; 0FFF00000, used
> MTRR #4 = 0E0000000, 01; 0F0000000, used
> MTRR #5 = 0F0000000, 06; 0F0000000, used
> MTRR #6 = 000000000, 06; 0E0000000, used
> MTRR #7 = 000000000, 00; 000000000, unused
> MTRR area E0000000-EFFFFFFFh was set to mode: WC
>
> And gues what? I got fast LFB even in pure DOS. So as you can see my tool
> set the MTRR for LFB properly (MTRR #4 = 0E0000000, 01; 0F0000000, used).
> But it seems to interfere with other MTRRs that was set by silly BIOS. I
> tried to clear them out 1 by 1 but didn't helped. Do you see the problem?
> Please help.
some MTRR entries are pushed down by NT4/VBEMP. Does the order make the different result?
I wonder if #0 to #2 can be combined into 1 entry and it is still work as expected?

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