linux-kernel - Re: [Xen-devel] [PATCH] x86 fixes for 3.3 impacting distros (v1).

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Message-ID: <4FEE2C4B.7040405@zytor.com>
Date:	Fri, 29 Jun 2012 15:29:31 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyclonus J <cyclonusj@...il.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	marmarek@...isiblethingslab.com, xen-devel@...ts.xensource.com,
	x86@...nel.org, Jason Garrett-Glaser <jason@...4.com>,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	mingo@...hat.com, tglx@...utronix.de,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Subject: Re: [Xen-devel] [PATCH] x86 fixes for 3.3 impacting distros (v1).

On 06/29/2012 02:52 PM, Cyclonus J wrote:
> 
> Peter,
> 
> hmm, It looks like option 1 doesn't have any perf regression, but it is still
> not acceptable? That is fine. If you prefer to have a software PAT table lookup, could you provide
> some details so I can try to get something align that direction?
> 

It has no perf regression, but it really buries deep in the code a
strange abstraction which only happens to work on Xen and is confusing
as hell.

The idea with a software PAT table is that the PAT numbers used by the
kernel should come from a table in the kernel instead of being
hard-coded.  That might take some work, and it remains to be seen if it
is practical.

It *may* be that we need to hard-code 0 as WB, still, but that should be
true on any sane platform.

	-hpa
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