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@xxxxxxxx> AuthorDate: Fri, 2 Nov 2012 14:21:23 +0000 Committer: Ingo Molnar <mingo@xxxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html