From d98d07ca7e0347d712d54a865af323c4aee04bc2 Mon Sep 17 00:00:00 2001
From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Tue, 27 Nov 2012 23:29:04 -0200
Subject: [PATCH] KVM: x86: update pvclock area conditionally, on cpu migration

As requested by Glauber, do not update kvmclock area on vcpu->pcpu
migration, in case the host has stable TSC.

This is to reduce cacheline bouncing.

Acked-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
---
 arch/x86/kvm/x86.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 422ef5ed21944..fd766214d9dad 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2627,7 +2627,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 			kvm_x86_ops->write_tsc_offset(vcpu, offset);
 			vcpu->arch.tsc_catchup = 1;
 		}
-		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+		/*
+		 * On a host with synchronized TSC, there is no need to update
+		 * kvmclock on vcpu->cpu migration
+		 */
+		if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
+			kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 		if (vcpu->cpu != cpu)
 			kvm_migrate_timers(vcpu);
 		vcpu->cpu = cpu;
-- 
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