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Subject: Re: [PATCH RFC 0/7] KVM: nVMX: enlightened VMCS initial
 implementation
To: Vitaly Kuznetsov <vkuznets@redhat.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <c5c1357d-c36a-38bf-6148-8ffb89a0290b@redhat.com>
Date: Thu, 21 Dec 2017 15:32:14 +0100
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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.

Paolo