Messages in this thread | | | Date | Fri, 25 Jan 2013 17:05:15 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [tip:x86/asm] x86/xor: Make virtualization friendly |
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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 <JBeulich@suse.com> >>> AuthorDate: Fri, 2 Nov 2012 14:21:23 +0000 >>> Committer: Ingo Molnar <mingo@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?
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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