Re: [Xen-devel][PATCH][RFC] SupportingEnlightenedWindows2008Server

["Ky Srinivasan" <ksrinivasan@xxxxxxxxxx>]

>>> On Tue, Apr 8, 2008 at  1:15 PM, in message
<C42166D1.16177%keir.fraser@xxxxxxxxxxxxx>, Keir Fraser
<keir.fraser@xxxxxxxxxxxxx> wrote: 
> On 8/4/08 18:03, "Ky Srinivasan" <ksrinivasan@xxxxxxxxxx> 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
> 
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