Re: [PATCH RFC 0/7] KVM: nVMX: enlightened VMCS initial implementation
From: Vitaly Kuznetsov
Date: Thu Dec 21 2017 - 10:08:49 EST
Paolo Bonzini <pbonzini@xxxxxxxxxx> 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.