On 2017/7/31 21:20, Paolo Bonzini wrote: > 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). > Hi Paolo, It seems that other architectures(e.g. arm/s390) needn't to cache the result, but x86 need, so I need to move 'in_kernmode' into kvm_vcpu_arch and only add this field to x86, right? > 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). In this approach, vmx_sched_out would only call vmx_get_cpl, isn't too redundant, because we can just call kvm_x86_ops->get_cpl instead at the right place? > This will cache the result until the next sched_in, so that 'until the next sched_in' --> Do we need to clear the result in sched in ? > kvm_vcpu_on_spin can use it. > > Paolo > > . > -- Regards, Longpeng(Mike)
