linux-kernel - [PATCH] KVM: LAPIC: Don't kick vCPU which is injecting already-expired timer

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Date:   Fri, 21 Aug 2020 17:17:34 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] KVM: LAPIC: Don't kick vCPU which is injecting already-expired timer

From: Wanpeng Li <wanpengli@...cent.com>

The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer 
fires on a different pCPU which vCPU is running on, we don't need this 
kick when injecting already-expired timer, this kick is expensive since 
memory barrier, rcu, preemption disable/enable operations. This patch 
reduces the overhead by don't kick vCPU which is injecting already-expired 
timer.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/lapic.c | 2 +-
 arch/x86/kvm/x86.c   | 5 +++--
 arch/x86/kvm/x86.h   | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 248095a..5b5ae66 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1642,7 +1642,7 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
 	}
 
 	atomic_inc(&apic->lapic_timer.pending);
-	kvm_set_pending_timer(vcpu);
+	kvm_set_pending_timer(vcpu, from_timer_fn);
 }
 
 static void start_sw_tscdeadline(struct kvm_lapic *apic)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 599d732..2a45405 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1778,10 +1778,11 @@ static s64 get_kvmclock_base_ns(void)
 }
 #endif
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
+void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick)
 {
 	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
-	kvm_vcpu_kick(vcpu);
+	if (should_kick)
+		kvm_vcpu_kick(vcpu);
 }
 
 static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 995ab69..0eaae9c 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -246,7 +246,7 @@ static inline bool kvm_vcpu_latch_init(struct kvm_vcpu *vcpu)
 	return is_smm(vcpu) || kvm_x86_ops.apic_init_signal_blocked(vcpu);
 }
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu);
+void kvm_set_pending_timer(struct kvm_vcpu *vcpu, bool should_kick);
 void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip);
 
 void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr);
-- 
2.7.4