linux-kernel - [PATCH RFC: kvm tsc virtualization 11/20] Use highest TSC frequency as reference clock

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Date:	Mon, 14 Dec 2009 18:08:38 -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>,
	Joerg Roedel <joerg.roedel@....com>,
	linux-kernel@...r.kernel.org, Dor Laor <dlaor@...hat.com>
Subject: [PATCH RFC: kvm tsc virtualization 11/20] Use highest TSC frequency as reference clock

If CPU frequency governors can change the TSC frequency, use
the highest possible frequency as the reference.

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 520ea6a..3c4266f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3701,7 +3701,15 @@ static void kvm_timer_init(void)
 	 * can change at any time.
 	 */
 	register_cpu_notifier(&kvm_x86_cpu_notifier);
+	ref_tsc_khz = tsc_khz;
 	if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+#ifdef CONFIG_CPU_FREQ
+		struct cpufreq_policy policy;
+
+		cpufreq_get_policy(&policy, get_cpu());
+		ref_tsc_khz = policy.cpuinfo.max_freq;
+		put_cpu();
+#endif
 		cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
 					  CPUFREQ_TRANSITION_NOTIFIER);
 		for_each_online_cpu(cpu) {
@@ -3718,7 +3726,6 @@ static void kvm_timer_init(void)
 			per_cpu(cpu_tsc_khz, cpu) = tsc_khz;
 	}
 	tsc_base_cpu = get_cpu();
-	ref_tsc_khz = per_cpu(cpu_tsc_khz, tsc_base_cpu);
 	resync(NULL);
 	put_cpu();
 }
-- 
1.6.5.2

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