KVM: Cap vcpu->halt_poll_ns before halting rather than after

Cap vcpu->halt_poll_ns based on the max halt polling time just before halting, rather than after the last halt. This arguably provides better accuracy if an admin disables halt polling in between halts, although the improvement is nominal. A side-effect of this change is that grow_halt_poll_ns() no longer needs to access vcpu->kvm->max_halt_poll_ns, which will be useful in a future commit where the max halt polling time can come from the module parameter halt_poll_ns instead. Signed-off-by: David Matlack <[email protected]> Message-Id: <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
sedwards · Nov 17, 2022 · 97b6847 · 97b6847
1 parent 6d3085e
commit 97b6847
Showing 1 changed file with 6 additions and 4 deletions.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -3377,9 +3377,6 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 	if (val < grow_start)
 		val = grow_start;
 
-	if (val > vcpu->kvm->max_halt_poll_ns)
-		val = vcpu->kvm->max_halt_poll_ns;
-
 	vcpu->halt_poll_ns = val;
 out:
 	trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
@@ -3492,11 +3489,16 @@ static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
 void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
 {
 	bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
-	bool do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
 	ktime_t start, cur, poll_end;
 	bool waited = false;
+	bool do_halt_poll;
 	u64 halt_ns;
 
+	if (vcpu->halt_poll_ns > vcpu->kvm->max_halt_poll_ns)
+		vcpu->halt_poll_ns = vcpu->kvm->max_halt_poll_ns;
+
+	do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
+
 	start = cur = poll_end = ktime_get();
 	if (do_halt_poll) {
 		ktime_t stop = ktime_add_ns(start, vcpu->halt_poll_ns);