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Subject: RE: e820 and shared VGA memory problem
Date: Thu, 18 Nov 2004 14:09:27 -0800
Message-ID: <88056F38E9E48644A0F562A38C64FB600360C709@scsmsx403.amr.corp.intel.com>
Thread-Topic: e820 and shared VGA memory problem
Thread-Index: AcTNuiJ/qRWudVE8QyqVIPuss+egZAAAIHog
From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: "Magnus Damm" <magnus.damm@gmail.com>, "Dave Jones" <davej@redhat.com>,
       <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1460
Lines: 33

 

>-----Original Message-----
>From: linux-kernel-owner@vger.kernel.org 
>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Magnus Damm
>Sent: Thursday, November 18, 2004 1:50 PM
>To: Dave Jones; Magnus Damm; linux-kernel@vger.kernel.org
>Subject: Re: e820 and shared VGA memory problem
>
>On Thu, 18 Nov 2004 16:44:31 -0500, Dave Jones 
><davej@redhat.com> wrote:
>> In the past such problems have been attributed to BIOS's not
>> setting up MTRRs correctly, or in extreme situations, running
>> out of available MTRRS.  How does /proc/mtrr look ?
>
>reg00: base=0x00000000 (   0MB), size=1024MB: write-back, count=1
>reg01: base=0x40000000 (1024MB), size= 512MB: write-back, count=1
>reg02: base=0x60000000 (1536MB), size= 256MB: write-back, count=1
>reg03: base=0x70000000 (1792MB), size= 128MB: write-back, count=1
>reg04: base=0x78000000 (1920MB), size=  64MB: write-back, count=1
>reg05: base=0x7c000000 (1984MB), size=  32MB: write-back, count=1

The issue is with the bad MTRR setting by BIOS.
It only sets 0-2016MB as write-back. 2016MB-2048MB is set as uncached.
Due to this whenever you use that memory you will see the slowness.
Probably BIOS is assuming that Video will always use 32MB.

-Venki
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