On 19/05/2016 15:27, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > If an emulated lapic timer will fire soon(in the scope of 10us the > base of dynamic halt-polling, lower-end of message passing workload > latency TCP_RR's poll time < 10us) we can treat it as a short halt, > and poll to wait it fire, the fire callback apic_timer_fn() will set > KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. > This can avoid context switch overhead and the latency which we wake > up vCPU. Would this work too and be simpler? diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4fd482fb9260..8d42f5304d94 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1964,16 +1964,12 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) old = val = vcpu->halt_poll_ns; grow = READ_ONCE(halt_poll_ns_grow); - /* 10us base */ - if (val == 0 && grow) - val = 10000; - else - val *= grow; + val *= grow; if (val > halt_poll_ns) val = halt_poll_ns; - vcpu->halt_poll_ns = val; + vcpu->halt_poll_ns = max(10000u, val); trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old); } @@ -1988,7 +1984,7 @@ static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu) else val /= shrink; - vcpu->halt_poll_ns = val; + vcpu->halt_poll_ns = max(10000u, val); trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old); } (Plus moving 10000 into a module parameter?) Can you measure higher CPU utilization than with your patch? David, what do you think? Thanks, Paolo -- 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
