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

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Date:	Wed, 21 Oct 2009 22:01:36 +0200
From:	Thomas Schlichter <thomas.schlichter@....de>
To:	Ingo Molnar <mingo@...e.hu>, Jan Beulich <JBeulich@...ell.com>
Cc:	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

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

OK, so I think the attached patches should do it. Hopefully I have addressed 
all your comments.

This series works for my test machine, without it, or without X running, I 
have these MTRR entries:
reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
reg01: base=0x06ff00000 ( 1791MB), size=    1MB, count=1: uncachable
reg02: base=0x070000000 ( 1792MB), size=  256MB, count=1: uncachable

With the patches applied and X running I get these:
reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
reg01: base=0x06ff00000 ( 1791MB), size=    1MB, count=1: uncachable
reg02: base=0x070000000 ( 1792MB), size=  256MB, count=1: uncachable
reg03: base=0x0d0000000 ( 3328MB), size=  256MB, count=1: write-combining

Best regards,
  Thomas

View attachment "0001-Make-num_var_ranges-accessible-outside-MTRR-code.patch" of type "text/x-patch" (1638 bytes)

View attachment "0002-Provide-per-file-private-data-for-bin-sysfs-files.patch" of type "text/x-patch" (2203 bytes)

View attachment "0003-Use-MTRR-for-pci_mmap_resource_wc-if-PAT-is-not-avai.patch" of type "text/x-patch" (5752 bytes)