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

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Message-ID: <20091021173514.GA32227@elte.hu>
Date:	Wed, 21 Oct 2009 19:35:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Thomas Schlichter <thomas.schlichter@....de>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Robert Hancock <hancockrwd@...il.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Tejun Heo <tj@...nel.org>, x86@...nel.org,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	dri-devel@...ts.sourceforge.net, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	Thomas Hellstrom <thellstrom@...are.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
	available


* Jan Beulich <JBeulich@...ell.com> wrote:

> > So if it's OK for Jan, I'll reduce the functionality again and use 
> > mtrr_add() instead. Btw. this simply means to drop 
> > mtrr_add_unaligned(), all the other parts are still required for 
> > reference counting and a proper mtrr_del() on file close.
> 
> I'm perfectly fine with just handling the aligned case, as long as the 
> code checks that the alignment constraints are met.

It could even emit a debug warning if they are not met - that way we'll 
see how important the unaligned case is.

	Ingo
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