SMT siblings share caches and other hardware, and busy halt polling will degrade its sibling performance if its sibling is working Sean Christopherson suggested as below: "Rather than disallowing halt-polling entirely, on x86 it should be sufficient to simply have the hardware thread yield to its sibling(s) via PAUSE. It probably won't get back all performance, but I would expect it to be close. This compiles on all KVM architectures, and AFAICT the intended usage of cpu_relax() is identical for all architectures." Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> --- diff v1: using cpu_relax, rather that stop halt-polling virt/kvm/kvm_main.c | 1 + 1 file changed, 1 insertion(+) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7d95126..1679728 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3110,6 +3110,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) ++vcpu->stat.generic.halt_poll_invalid; goto out; } + cpu_relax(); poll_end = cur = ktime_get(); } while (kvm_vcpu_can_poll(cur, stop)); } -- 2.9.4
