On 13.03.20 13:40, Michael Mueller wrote: > A statistical analysis shows that in most cases when deliverable_irqs() > is called, no interrupts are pending. (see: early exit ratio) > > The data was sampled during an iperf3 run over virtio_net > between one guest and the host. > > deliverable_irqs() > called = 3145123 > by kvm_s390_vcpu_has_irq() = 3005581 (95.56%) > by kvm_arch_vcpu_runnable() = 3005578 (95.56%) > by kvm_s390_handle_wait() = 1219331 (38.76%) > by kvm_vcpu_check_block() = 2943565 (93.59%) > by kvm_cpu_block(1) = 2826431 (89.86%) > by kvm_cpu_block(2) = 117136 (3.72%) > by kvm_arch_dy_runnable() = 0 (0%) > by kvm_arch_setup_async_pf() = 0 (0%) > by handle_stop() = 0 (0%) > by kvm_s390_deliver_pending_interrupt() = 139542 (4.43%) > irqs_delivered = (0:15917 1:61810 2:1 3:0 4:0 x:0) > irqs_pending = (0:15917 1:61722 2:86 3:1 4:0 x:0) > early exit = 3021787 (96.07%) > pending irqs = 123237 (3.91%) > > Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx> > --- > arch/s390/kvm/interrupt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index 028167d6eacd..c34d62b4209e 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -369,7 +369,7 @@ static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu) > unsigned long active_mask; > > active_mask = pending_irqs(vcpu); > - if (!active_mask) > + if (likely(!active_mask)) I have never been a fan of the likely/unlikely name. Instead this should have been fastpath/slowpath. And with likely actually meaning fastpath this patch makes sense. I guess it does not change the performance as the branch predictor is doing its job most of the time. So I assume it would only be visible when there is contention in the host. Tentatively Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> will have a look at the code.
