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Re: [Xen-devel][PATCH][RFC] Supporting EnlightenedWindows2008Server

To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel][PATCH][RFC] Supporting EnlightenedWindows2008Server
From: "Ky Srinivasan" <ksrinivasan@xxxxxxxxxx>
Date: Tue, 08 Apr 2008 11:13:33 -0600
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>>> On Mon, Apr 7, 2008 at 11:15 AM, in message
<C41FF920.1EDFD%keir.fraser@xxxxxxxxxxxxx>, Keir Fraser
<keir.fraser@xxxxxxxxxxxxx> wrote: 
> On 7/4/08 15:28, "Ky Srinivasan" <ksrinivasan@xxxxxxxxxx> wrote:
>>> It's certainly quite a bit shorter which is good. For the remaining stuff,
>>> do you have empirical evidence that performance is improved by it?
>> I do. On the NetBench runs we did, we were seeing close to 10% improvement. 
> I
>> will keep you posted on other benchmark results as they become available.
>> Furthermore, as MSFT defines new enlightenments, we can implement those
>> cleanly within this body of code. Additionally, there is value in claiming
>> that we support all the enlightenments needed for hosting enlightened win 
> 2008
>> servers.
> Do you know which hypercalls that benefit comes from? HV_GET_VP_REGISTERS see 
> no reason to
> support more hypercalls than necessary (I certainly don't see the value in
> that as an end in itself).

Agreed. Based on the latest hyperv V spec, I think only the following 
hypercalls make sense for an enlightened guest:

This is implemented in the patches I have submitted. This hypercall, currently 
is not used by the currently shipping windows 2008 server.

I only have stub for these hypercalls (not implemented). Current windows 2008 
server does not use these hypercalls.

3) HV_SWITCH_VA: I have implemented this hypercall.

I had implemented these hypercalls originally. In the current patch set, I have 
stubbed out these hypercalls. 

In addition to the hypercalls, Hyper V also surfaces functionality via 
synthetic MSRs and CPUID leaves.
I have implemented all the relevant MSRs and CPUID leaves. 

>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).


K. Y
>  --   Keir

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