linux-kernel - Re: [RFC Patch] use MTRR for write combining if PAT is not available

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Message-ID: <20091011074045.GA6555@elte.hu>
Date:	Sun, 11 Oct 2009 09:40:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Thomas Schlichter <thomas.schlichter@....de>,
	linux-kernel@...r.kernel.org,
	Thomas Hellstrom <thellstrom@...are.com>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
	available


* Arjan van de Ven <arjan@...ux.intel.com> wrote:

> Thomas Schlichter wrote:
>
>> Hmm, my CPU (VIA Nano) seems to support PAT, but Ubuntu disables this
>> feature in its kernel config. I'm using 9.04, but even 9.10 will have PAT
>> disabled:
>
> that sounds like a bad idea. But to each distro their own I suppose.
>
>
>>
>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-
>> karmic.git;a=blob;f=debian.master/config/config.common.ubuntu;h=a43cbabd02bfdf5412de6fea232db86aa5d3e742;hb=HEAD
>
>> So, convincing Ubuntu to enable PAT would be a workaround, but I think
>> the problem would still exist and should be fixed.
>
> I think it's time to get rid of CONFIG_PAT at all.. and just have it 
> be there. Making 10+ year old CPU features that are essential 
> functionality a config option... ... not a good idea to be honest.

Mind sending a patch that makes the configurability of PAT dependent on 
EMBEDDED or so? There's still the nopat boot option so it can still be 
configured by a distro if it wishes to.

	Ingo
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