Messages in this thread | | | Subject | Re: [RFC] KVM: optimize the kvm_vcpu_on_spin | From | Paolo Bonzini <> | Date | Mon, 31 Jul 2017 15:20:11 +0200 |
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On 31/07/2017 14:27, David Hildenbrand wrote: >> I'm not sure whether the operation of get the vcpu's priority-level is >> expensive on all architectures, so I record it in kvm_sched_out() for >> minimal the extra cycles cost in kvm_vcpu_on_spin(). >> > as you only care for x86 right now either way, you can directly optimize > here for the good (here: x86) case (keeping changes and therefore > possible bugs minimal).
I agree with Cornelia that this is inconsistent, so you shouldn't update me->in_kernmode in kvm_vcpu_on_spin. However, get_cpl requires vcpu_load on Intel x86, so Mike's patch is necessary (vmx_get_cpl -> vmx_read_guest_seg_ar -> vmcs_read32).
Alternatively, we can add a new callback kvm_x86_ops->sched_out to x86 KVM, and call vmx_get_cpl from the Intel implementation (vmx_sched_out). This will cache the result until the next sched_in, so that kvm_vcpu_on_spin can use it.
Paolo
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