linux-kernel - [KVM timekeeping 26/35] Catchup slower TSC to guest rate

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Date:	Thu, 19 Aug 2010 22:07:40 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	kvm@...r.kernel.org
Cc:	Zachary Amsden <zamsden@...hat.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: [KVM timekeeping 26/35] Catchup slower TSC to guest rate

Use the catchup code to continue adjusting the TSC when
running at lower than the guest rate

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
---
 arch/x86/kvm/x86.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a4215d7..086d56a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1013,8 +1013,11 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 			kvm_x86_ops->adjust_tsc_offset(v, tsc-tsc_timestamp);
 	}
 	local_irq_restore(flags);
-	if (catchup)
+	if (catchup) {
+		if (this_tsc_khz < v->kvm->arch.virtual_tsc_khz)
+			vcpu->tsc_rebase = 1;
 		return 0;
+	}
 
 	/*
 	 * Time as measured by the TSC may go backwards when resetting the base
@@ -5022,6 +5025,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	kvm_guest_exit();
 
+	/* Running on slower TSC without kvmclock, we must bump TSC */
+	if (vcpu->arch.tsc_rebase)
+		kvm_request_clock_update(vcpu);
+
 	preempt_enable();
 
 	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
-- 
1.7.1

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