It adds substantial boot time, and it has no value when the cache priority rules force the non-cache-polluting version even if somewhat slower... which can and does happen.
Jan Beulich <jbeul...@suse.com> wrote: >>>> On 25.01.13 at 23:11, "H. Peter Anvin" <h...@zytor.com> 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. > >I don't follow: The patch doesn't penalize anyone, it merely >widens the set of methods tried on virtualized platforms. I.e. >if other hypervisors have no problem here, then the best >performing one should still turn out to be the SSE or AVX one. >Or if it doesn't, it ought to be to their advantage (I would even >question why this extra probing isn't done on native too, e.g. >to cope with eventual bad vector implementations, say on >low-power/low-cost CPUs). > >Jan -- Sent from my mobile phone. Please excuse brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
