[PATCH 1/1] KVM: shrink halt polling even more for invalid wakeups

[Christian Borntraeger <borntraeger@de.ibm.com>]

commit 3491caf2755e ("KVM: halt_polling: provide a way to qualify
 wakeups during poll") added more aggressive shrinking of the
polling interval if the wakeup did not match some criteria. This
still allows to keep polling enabled if the polling time was
smaller that the current max poll time (block_ns <= vcpu->halt_poll_ns).
Performance measurement shows that even more aggressive shrinking
(shrink polling on any invalid wakeup) reduces absolute and relative
(to the workload) CPU usage even further.

Cc: David Matlack <dmatlack@google.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 virt/kvm/kvm_main.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fbd7698..dec1ed2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2055,12 +2055,13 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 out:
 	block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
 
-	if (halt_poll_ns) {
+	if (!vcpu_valid_wakeup(vcpu))
+		 shrink_halt_poll_ns(vcpu);
+	else if (halt_poll_ns) {
 		if (block_ns <= vcpu->halt_poll_ns)
 			;
 		/* we had a long block, shrink polling */
-		else if (!vcpu_valid_wakeup(vcpu) ||
-			(vcpu->halt_poll_ns && block_ns > halt_poll_ns))
+		else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
 			shrink_halt_poll_ns(vcpu);
 		/* we had a short halt and our poll time is too small */
 		else if (vcpu->halt_poll_ns < halt_poll_ns &&
-- 
2.5.5