linux-kernel - Re: [tip:x86/asm] x86/xor: Make virtualization friendly

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Date:	Fri, 25 Jan 2013 14:11:09 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	konrad.wilk@...cle.com, torvalds@...ux-foundation.org,
	JBeulich@...e.com, jbeulich@...e.com, tglx@...utronix.de
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/asm] x86/xor: Make virtualization friendly

On 01/25/2013 02:43 AM, tip-bot for Jan Beulich wrote:
> Commit-ID:  05fbf4d6fc6a3c0c3e63b77979c9311596716d10
> Gitweb:     http://git.kernel.org/tip/05fbf4d6fc6a3c0c3e63b77979c9311596716d10
> Author:     Jan Beulich <JBeulich@...e.com>
> AuthorDate: Fri, 2 Nov 2012 14:21:23 +0000
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 25 Jan 2013 09:23:51 +0100
> 
> x86/xor: Make virtualization friendly
> 
> In virtualized environments, the CR0.TS management needed here
> can be a lot slower than anticipated by the original authors of
> this code, which particularly means that in such cases forcing
> the use of SSE- (or MMX-) based implementations is not desirable
> - actual measurements should always be done in that case.
> 
> For consistency, pull into the shared (32- and 64-bit) header
> not only the inclusion of the generic code, but also that of the
> AVX variants.
> 

This patch is wrong and should be dropped.  I verified it with the KVM
people that they do NOT want this change.  It is a Xen-specific problem.

	-hpa


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