Re: [PATCH RFC 0/7] KVM: nVMX: enlightened VMCS initial implementation

Vitaly Kuznetsov
2017-12-21T15:08:44Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 21/12/2017 13:50, Vitaly Kuznetsov wrote:
>> I'm back with (somewhat frustrating) results (E5-2603):
>
> v4 (that would be Broadwell)?
>

Sorry, v3, actually. Haswell. (the first one supporting vmcs shadowing afaiu).

>> 1) Windows on Hyper-V (no nesting): 1350 cycles
>>
>> 2) Windows on Hyper-V on Hyper-V: 8600
>>
>> 3) Windows on KVM (no nesting): 1150 cycles
>>
>> 4) Windows on Hyper-V on KVM (no enlightened VMCS): 18200
>>
>> 5) Windows on Hyper-V on KVM (enlightened VMCS): 17100
>
> What version were you using for KVM? There are quite a few nested virt
> optimizations in kvm/queue (which may make enlightened VMCS both more or
> less efficient).

This is kvm/queue and I rebased enlightened VMCS patches to it.

>
> In particular, with latest kvm/queue you could try tracing vmread and
> vmwrite vmexits, and see if you get any. If you do, that might be an
> easy few hundred cycles savings.

Will do.

--
Vitaly