Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Fri,  8 Oct 2021 19:12:00 -0700
In-Reply-To: <20211009021236.4122790-1-seanjc@google.com>
Message-Id: <20211009021236.4122790-8-seanjc@google.com>
Mime-Version: 1.0
References: <20211009021236.4122790-1-seanjc@google.com>
Subject: [PATCH v2 07/43] KVM: Reconcile discrepancies in halt-polling stats
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>,
        Anup Patel <anup.patel@wdc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        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>,
        Atish Patra <atish.patra@wdc.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, kvm-riscv@lists.infradead.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        David Matlack <dmatlack@google.com>,
        Oliver Upton <oupton@google.com>,
        Jing Zhang <jingzhangos@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Move the halt-polling "success" and histogram stats update into the
dedicated helper to fix a discrepancy where the success/fail "time" stats
consider polling successful so long as the wait is avoided, but the main
"success" and histogram stats consider polling successful if and only if
a wake event was detected by the halt-polling loop.

Move halt_attempted_poll to the helper as well so that all the stats are
updated in a single location.  While it's a bit odd to update the stat
well after the fact, practically speaking there's no meaningful advantage
to updating before polling.

Note, there is a functional change in addition to the success vs. fail
change.  The histogram updates previously called ktime_get() instead of
using "cur".  But that change is desirable as it means all the stats are
now updated with the same polling time, and avoids the extra ktime_get(),
which isn't expensive but isn't free either.

Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4dfcd736b274..1292c7876d3f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3204,12 +3204,23 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
 					  ktime_t end, bool success)
 {
+	struct kvm_vcpu_stat_generic *stats = &vcpu->stat.generic;
 	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;
+	++vcpu->stat.generic.halt_attempted_poll;
+
+	if (success) {
+		++vcpu->stat.generic.halt_successful_poll;
+
+		if (!vcpu_valid_wakeup(vcpu))
+			++vcpu->stat.generic.halt_poll_invalid;
+
+		stats->halt_poll_success_ns += poll_ns;
+		KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_success_hist, poll_ns);
+	} else {
+		stats->halt_poll_fail_ns += poll_ns;
+		KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_fail_hist, poll_ns);
+	}
 }
 
 /*
@@ -3230,30 +3241,16 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	if (do_halt_poll) {
 		ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
 
-		++vcpu->stat.generic.halt_attempted_poll;
 		do {
 			/*
 			 * This sets KVM_REQ_UNHALT if an interrupt
 			 * arrives.
 			 */
-			if (kvm_vcpu_check_block(vcpu) < 0) {
-				++vcpu->stat.generic.halt_successful_poll;
-				if (!vcpu_valid_wakeup(vcpu))
-					++vcpu->stat.generic.halt_poll_invalid;
-
-				KVM_STATS_LOG_HIST_UPDATE(
-				      vcpu->stat.generic.halt_poll_success_hist,
-				      ktime_to_ns(ktime_get()) -
-				      ktime_to_ns(start));
+			if (kvm_vcpu_check_block(vcpu) < 0)
 				goto out;
-			}
 			cpu_relax();
 			poll_end = cur = ktime_get();
 		} while (kvm_vcpu_can_poll(cur, stop));
-
-		KVM_STATS_LOG_HIST_UPDATE(
-				vcpu->stat.generic.halt_poll_fail_hist,
-				ktime_to_ns(ktime_get()) - ktime_to_ns(start));
 	}
 
 
-- 
2.33.0.882.g93a45727a2-goog