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From: Arjan van de Ven <>
To: "Diego M. Vadell" <>
Cc: Linux Kernel <>
Subject: Re: PAT and MTRRs
Date: Sun, 26 Oct 2008 17:12:10 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, 26 Oct 2008 22:46:21 -0100
"Diego M. Vadell" <> wrote:

> Hello,
>    I have 6 identical PCs (HPC cluster) with MTRR problems. In older
> kernels, I had to use "mem=3300M", or else, I would get a very slowly
> boot (as when you run out of MTRRs). 
>    So I thought that PAT would make this lack of MTRRs problem go
> away, and upgraded to and, but it didn't: I still
> get (from dmesg)
> x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
> WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing 704MB
> of RAM.
>    Most probably, I understood wrong. I read's article [1]
> about PAT several times, Documentation/x86/pat.txt , tried to use
> mtrr_chunk_size= and mtrr_gran_size= in various combinations (as
> discussed in this LKML thread [2]), but I still don't get it.
>    So, what did I miss? Am I wrong thinking that PAT is a better MTRR
> (wrt setting the cache type of the RAM)? 

PAT can't make memory cachable that the MTRR's have as uncachable.
What PAT *can* do is, within an MTRR, do fine grained mapping...

Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 

  reply	other threads:[~2008-10-27  0:12 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-26 23:46 Diego M. Vadell
2008-10-27  0:12 ` Arjan van de Ven [this message]
2008-10-27  0:21   ` H. Peter Anvin
2008-10-27  0:34     ` Arjan van de Ven
2008-10-27  0:38       ` H. Peter Anvin
2008-10-27  5:17 ` Yinghai Lu
2008-10-31 22:42   ` Diego M. Vadell
2008-10-31 23:19     ` Yinghai Lu
2008-10-31 23:35     ` Yinghai Lu
2008-11-11 14:30       ` Diego M. Vadell

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