From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754344Ab3AZBFn (ORCPT ); Fri, 25 Jan 2013 20:05:43 -0500 Received: from terminus.zytor.com ([198.137.202.10]:48420 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753496Ab3AZBFl (ORCPT ); Fri, 25 Jan 2013 20:05:41 -0500 Message-ID: <51032BCB.5070506@zytor.com> Date: Fri, 25 Jan 2013 17:05:15 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: "H. Peter Anvin" CC: mingo@kernel.org, linux-kernel@vger.kernel.org, konrad.wilk@oracle.com, torvalds@linux-foundation.org, JBeulich@suse.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, Marcelo Tosatti , "K. Y. Srinivasan" , Haiyang Zhang Subject: Re: [tip:x86/asm] x86/xor: Make virtualization friendly References: <5093E4F302000078000A6162@nat28.tlf.novell.com> <510302FD.3090009@zytor.com> <510303F8.1080105@zytor.com> In-Reply-To: <510303F8.1080105@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/25/2013 02:15 PM, H. Peter Anvin wrote: > On 01/25/2013 02:11 PM, H. Peter Anvin wrote: >> 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 >>> AuthorDate: Fri, 2 Nov 2012 14:21:23 +0000 >>> Committer: Ingo Molnar >>> 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. >> > > FWIW: I have dropped this patch from tip:x86/asm. > The bottom line, I guess, is that we need something like cpu_has_slow_kernel_fpu or something like that, and set it for specifically affected hypervisors? Do we know if Hyper-V has performance issues with CR0.TS? -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.