Ky Srinivasan
2008-Apr-13 19:05 UTC
Re: [Xen-devel][PATCH][RFC] SupportingEnlightenedWindows2008Server
>>> On Tue, Apr 8, 2008 at 1:15 PM, in message<C42166D1.16177%keir.fraser@eu.citrix.com>, Keir Fraser <keir.fraser@eu.citrix.com> wrote:> On 8/4/08 18:03, "Ky Srinivasan" <ksrinivasan@novell.com> wrote: > >> From a performance point of view, I think the MSR access to APIC registers > are >> the most important. As far as hypercalls go, the only one currently >> implemented is the hypercall to change the page table base. Some of the > other >> synthetic MSRs support features that the current windows 2008 server > currently >> is not using (timeouts for example). > > That''s a bit surprising since w2k8 probably accesses the TPR via %cr8, for > which we implement vmexit mitigation. The only other APIC register that is > often accessed is EOI. We can''t avoid the vmexit for that, and the extra > cost of not having an explicit MSR for it is a run through the mmio > emulator. I''d be surprised if avoiding the run through the emulator per > interrupt was that much of a win. > > Anyhow, you should be able to switch off HyperV features selectively, as > advertised to the domU HVM guest, and see which ones make a difference to > performance.The benchmark was run a while ago on some very early sles10 sp2 bits (late last fall/winter). It is by selectively enabling HyperV functionality that I concluded that APIC MSR access was the most important enlightenment based on NetBench results. We are in the process of running a range of benchmarks. I will keep you posted. Regards, K. Y> > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel