> -----Original Message----- > From: H. Peter Anvin [mailto:h...@zytor.com] > Sent: Friday, January 25, 2013 8:05 PM > To: H. Peter Anvin > Cc: mi...@kernel.org; linux-kernel@vger.kernel.org; konrad.w...@oracle.com; > torva...@linux-foundation.org; jbeul...@suse.com; t...@linutronix.de; linux- > tip-comm...@vger.kernel.org; Marcelo Tosatti; KY Srinivasan; Haiyang Zhang > Subject: Re: [tip:x86/asm] x86/xor: Make virtualization friendly > > 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 <jbeul...@suse.com> > >>> AuthorDate: Fri, 2 Nov 2012 14:21:23 +0000 > >>> Committer: Ingo Molnar <mi...@kernel.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. > >> > > > > 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?
Checking with the Hyper-V developers, Hyper-V does not have performance issues With CR0.TS Regards, K. Y > > -hpa > > -- > H. Peter Anvin, Intel Open Source Technology Center > I work for Intel. I don't speak on their behalf. > >
