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

From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
	kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
	linux-kernel@vger.kernel.org, David Matlack <dmatlack@google.com>,
	Jing Zhang <jingzhangos@google.com>
Subject: [PATCH 03/14] KVM: Refactor and document halt-polling stats update helper
Date: Fri, 24 Sep 2021 17:55:17 -0700	[thread overview]
Message-ID: <20210925005528.1145584-4-seanjc@google.com> (raw)
In-Reply-To: <20210925005528.1145584-1-seanjc@google.com>

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@google.com>
---
 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)
 	kvm_arch_vcpu_unblocking(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)) {
-- 
2.33.0.685.g46640cef36-goog

