>>> On Wed, Feb 20, 2008 at 4:44 AM, in message
<C3E1A703.1CB24%Keir.Fraser@xxxxxxxxxxxx>, Keir Fraser
> On 19/2/08 22:11, "Ky Srinivasan" <ksrinivasan@xxxxxxxxxx> wrote:
>> B) Implement an adapter that implements the required Hyper- V functionality.
>> We have implemented only a subset of Hyper- V functionality that is required
>> for enlightened windows 2008 guest today. However, we have the framework in
>> place to implement any additional functionality that the windows guests may
>> leverage going forward. The framework is extensible and one can easily
>> implement OS specific enlightenments.
> The appearance is that you hook on every significant emulation point in the
> HVM code and implement a shadow hypervisor. Is that an accurate description?
My initial goal was to get a framework in place where one could implement any
OS specific enhancements without cluttering up the rest of the Xen code. To
that end, this code does hook into various emulation points of interest in the
hvm code. A secondary goal was to minimize the changes to the base Xen code.
Furthermore, I wanted to reuse as much of the base Xen code as possible. So, I
would not characterize this as a shadow hypervisor, but rather as an adapter
that bridges the semantic gap between the APIs of interest in Hyper-V and Xen.
> What performance wins do you get from Hyper- V emulation, ignoring the
> obvious wins you will get from installing PV I/O drivers? I think this is a
> particularly interesting question since it was our impression that the PV
> memory- management interfaces, which you appear to jump through hoops to
> support, were not of much benefit with Xen's more sophisticated pagetable
> algorithm (or with Intel EPT or AMD NPT).
We have done very minimal performance evaluation to date. On NetBench I have
seen a 10% improvement. You are right, TLB flush enlightenments did not make
much of a difference. These results are on a uniprocessor configuration. Of the
enlightenments, MSR based APIC access made the most difference. Going forward,
we will be doing a more comprehensive performance evaluation with the goal of
having parity with the MS platform.
> -- Keir
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