Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> writes: > Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > >> On 18/12/2017 18:17, Vitaly Kuznetsov wrote: >>> The original author of these patches does no longer work at Red Hat, I >>> agreed to take this over and send upstream. Here is his original >>> description: >>> >>> "Makes KVM implement the enlightened VMCS feature per Hyper-V TLFS 5.0b. >>> I've measured about %5 improvement in cost of a nested VM exit (Hyper-V >>> enabled Windows Server 2016 nested in KVM)." >> >> Can you try reproducing this and see how much a simple CPUID loop costs in: >> >> * Hyper-V on Hyper-V (with enlightened VMCS, as a proxy for a full >> implementation including the clean fields mask) >> >> * Hyper-V on KVM, with and without enlightened VMCS >> >> The latest kvm/queue branch already cut a lot of the cost of a nested VM >> exit (from ~22000 to ~14000 clock cycles for KVM on KVM), so we could >> also see if Hyper-V needs shadowing of more fields. > > I tested this series before sending out and was able to reproduce said > 5% improvement with the feature (but didn't keep record of clock > cycles). I'll try doing tests you mentioned on the same hardware and > come back with the result. Hopefully I'll manage that before holidays. I'm back with (somewhat frustrating) results (E5-2603): 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 -- Vitaly
