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

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Date:	Wed, 21 Oct 2009 13:57:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Schlichter <thomas.schlichter@....de>
Cc:	Jan Beulich <JBeulich@...ell.com>,
	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


* Thomas Schlichter <thomas.schlichter@....de> wrote:

> Jan Beulich wrote:
>
> > Functionality-wise this looks fine to me; whether the core sysfs 
> > changes are acceptable I can't judge, though.
> 
> OK, I think I should have addressed your comments. Unfortunately I had 
> to use a little "hack" to make pci_mmap_page_range() work for sysfs 
> and proc. I placed a "private" pointer in the beginning of both 
> per-file private structures. So this pointer can be accessed 
> independent from the caller. I hope this is acceptable.
> 
> I dropped the ioremap() and set_memory_wc() patches, I could not 
> implement reference counting for them and it may interact too much 
> with existing GPU drivers.
> 
> Again, this series should not change the current behavior if either 
> MTRR is disabled or PAT is enabled. But it helps in the case that MTRR 
> is enabled and PAT is not available.
> 
> What should be done now to get this series on the right "track"?

Can we eliminate mtrr_add_unaligned() as Suresh suggested, and still 
make it work on your testbox?

Once that's done i'll look at putting it into the x86 tree for testing. 
The acks of Suresh/Venki/Jan would be nice to have.

	Ingo
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