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Message-Id: <20210925005528.1145584-13-seanjc@google.com>
Date: Fri, 24 Sep 2021 17:55:26 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
Paul Mackerras <paulus@...abs.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
David Hildenbrand <david@...hat.com>,
Cornelia Huck <cohuck@...hat.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
linux-mips@...r.kernel.org, kvm@...r.kernel.org,
kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
David Matlack <dmatlack@...gle.com>,
Jing Zhang <jingzhangos@...gle.com>
Subject: [PATCH 12/14] KVM: Don't redo ktime_get() when calculating
halt-polling stop/deadline
Calculate the halt-polling "stop" time using "cur" instead of redoing
ktime_get(). In the happy case where hardware correctly predicts
do_halt_poll, "cur" is only a few cycles old. And if the branch is
mispredicted, arguably that extra latency should count toward the
halt-polling time.
In all likelihood, the numbers involved are in the noise and either
approach is perfectly ok.
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2980d2b88559..80f78daa6b8d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3267,7 +3267,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
start = cur = poll_end = ktime_get();
if (do_halt_poll) {
- ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
+ ktime_t stop = ktime_add_ns(cur, vcpu->halt_poll_ns);
do {
/*
--
2.33.0.685.g46640cef36-goog
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