From 62bea5bff486644ecf363fe8a1a2f6f32c614a49 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 15 Sep 2015 18:27:57 +0200 Subject: KVM: add halt_attempted_poll to VCPU stats This new statistic can help diagnosing VCPUs that, for any reason, trigger bad behavior of halt_poll_ns autotuning. For example, say halt_poll_ns = 480000, and wakeups are spaced exactly like 479us, 481us, 479us, 481us. Then KVM always fails polling and wastes 10+20+40+80+160+320+480 = 1110 microseconds out of every 479+481+479+481+479+481+479 = 3359 microseconds. The VCPU then is consuming about 30% more CPU than it would use without polling. This would show as an abnormally high number of attempted polling compared to the successful polls. Acked-by: Christian Borntraeger Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 1 + 1 file changed, 1 insertion(+) (limited to 'virt') diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9af68db73c6a..04146a2e1d81 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2004,6 +2004,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) if (vcpu->halt_poll_ns) { ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); + ++vcpu->stat.halt_attempted_poll; do { /* * This sets KVM_REQ_UNHALT if an interrupt -- cgit v1.2.3-58-ga151