2016-12-14 13:59+0300, Denis Plotnikov: > When processing KVM_REQ_EVENT, apic_update_ppr is called which may set > KVM_REQ_EVENT again if the recalculated value of PPR becomes smaller > than the previous one. This results in cancelling the guest entry and > reiterating in vcpu_enter_guest. > > However this is unnecessary because at this point KVM_REQ_EVENT is > already being processed and there are no other changes in the lapic > that may require full-fledged state recalculation. > > This situation is often hit on systems with TPR shadow, where the > TPR can be updated by the guest without a vmexit, so that the first > apic_update_ppr to notice it is exactly the one called while > processing KVM_REQ_EVENT. > > To avoid it, introduce a parameter in apic_update_ppr allowing to > suppress setting of KVM_REQ_EVENT, and use it on the paths called from > KVM_REQ_EVENT processing. > Also add the parameter to kvm_cpu_get_interrupt to be passed through > to apic_update_ppr to make sure the supression of KVM_REQ_EVENT is done > in the KVM_REQ_EVENT processing path only. > > This microoptimization gives 10% performance increase on a synthetic > test doing a lot of IPC in Windows using window messages. > > Reviewed-by: Roman Kagan <rkagan@xxxxxxxxxxxxx> > Signed-off-by: Denis Plotnikov <dplotnikov@xxxxxxxxxxxxx> > --- It is not pretty, but desirable, Reviewed-by: Radim Krčmář <rkrcmar@xxxxxxxxxx> Thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
