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

From: Paolo Bonzini
Date: Thu Dec 21 2017 - 09:32:31 EST

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

v4 (that would be Broadwell)?

> 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).

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.