linux-kernel - Re: x86_64 ten times slower than i386

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Date:	Mon, 05 Nov 2007 11:11:19 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bo Brantén <bosse@....umu.se>
CC:	linux-kernel@...r.kernel.org
Subject: Re: x86_64 ten times slower than i386

Bo Brantén wrote:
> On Mon, 5 Nov 2007, H. Peter Anvin wrote:
> 
>>> reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
>>> reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
>>> reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
>>> reg03: base=0xcf800000 (3320MB), size=   8MB: uncachable, count=1
>>> reg04: base=0xcf700000 (3319MB), size=   1MB: uncachable, count=1
>>> reg05: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
>>> reg06: base=0x120000000 (4608MB), size= 128MB: write-back, count=1
>>
>> What does your e820 map look like?
> 
> BIOS-provided physical RAM map:
>  BIOS-e820: 0000000000000000 - 000000000008f000 (usable)
>  BIOS-e820: 000000000008f000 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
>  BIOS-e820: 0000000000100000 - 00000000cf561000 (usable)
>  BIOS-e820: 00000000cf561000 - 00000000cf56e000 (reserved)
>  BIOS-e820: 00000000cf56e000 - 00000000cf637000 (usable)
>  BIOS-e820: 00000000cf637000 - 00000000cf6e9000 (ACPI NVS)
>  BIOS-e820: 00000000cf6e9000 - 00000000cf6ed000 (usable)
>  BIOS-e820: 00000000cf6ed000 - 00000000cf6f2000 (ACPI data)
>  BIOS-e820: 00000000cf6f2000 - 00000000cf6f3000 (usable)
>  BIOS-e820: 00000000cf6f3000 - 00000000cf6ff000 (ACPI data)
>  BIOS-e820: 00000000cf6ff000 - 00000000cf700000 (usable)
>  BIOS-e820: 00000000cf700000 - 00000000d0000000 (reserved)
>  BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)
>  BIOS-e820: 0000000100000000 - 000000012c000000 (usable)
> 

Okay, the bug is that the range 4736MB to 4800MB is marked USABLE in the 
map, but isn't covered by any MTRR.  Your BIOS is still buggy.

echo 'base=0x128000000 size=0x4000000 type=write-back' > /proc/mtrr

... should fix it since you still have an unused MTRR.  It might make X 
unhappy, though, since it may want an MTRR to mark the framebuffer 
write-combining.

	-hpa
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