[PATCH 03/14] KVM: Refactor and document halt-polling stats update helper

From: Sean Christopherson
Date: Fri Sep 24 2021 - 20:55:50 EST

Add a comment to document that halt-polling is considered successful even
if the polling loop itself didn't detect a wake event, i.e. if a wake
event was detect in the final kvm_vcpu_check_block(). Invert the param
to the update helper so that the helper is a dumb function that is "told"
whether or not polling was successful, as opposed to having it determinine
success/failure based on blocking behavior.

Opportunistically tweak the params to the update helper to reduce the
line length for the call site so that it fits on a single line, and so
that the prototype conforms to the more traditional kernel style.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
virt/kvm/kvm_main.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8b33f5045b4d..12fe91a0a4c8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3199,13 +3199,15 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
return ret;

-static inline void
-update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited)
+static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
+ ktime_t end, bool success)
- if (waited)
- vcpu->stat.generic.halt_poll_fail_ns += poll_ns;
- else
+ u64 poll_ns = ktime_to_ns(ktime_sub(end, start));
+ if (success)
vcpu->stat.generic.halt_poll_success_ns += poll_ns;
+ else
+ vcpu->stat.generic.halt_poll_fail_ns += poll_ns;

@@ -3274,9 +3276,13 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
block_ns = ktime_to_ns(cur) - ktime_to_ns(start);

+ /*
+ * Note, halt-polling is considered successful so long as the vCPU was
+ * never actually scheduled out, i.e. even if the wake event arrived
+ * after of the halt-polling loop itself, but before the full wait.
+ */
if (do_halt_poll)
- update_halt_poll_stats(
- vcpu, ktime_to_ns(ktime_sub(poll_end, start)), waited);
+ update_halt_poll_stats(vcpu, start, poll_end, !waited);

if (halt_poll_allowed) {
if (!vcpu_valid_wakeup(vcpu)) {