linux-kernel - [PATCH RFC: kvm tsc virtualization 04/20] Synchronize TSC when a new CPU comes up

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Message-Id: <1260850127-9766-5-git-send-email-zamsden@redhat.com>
Date:	Mon, 14 Dec 2009 18:08:31 -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 04/20] Synchronize TSC when a new CPU comes up

The loop is written to only work when one master and one slave
enter simultaneously, so properly protect it, and call it when
adding new CPUs.

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
---
 arch/x86/kvm/x86.c |   43 ++++++++++++++++++++++++++++++++-----------
 1 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 95e43b9..a599c78 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -729,6 +729,7 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *
 		 hv_clock->tsc_to_system_mul);
 }
 
+DEFINE_SPINLOCK(kvm_tsc_lock);
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_multiplier);
 static DEFINE_PER_CPU(int, cpu_tsc_shift);
@@ -921,6 +922,21 @@ static void kvm_sync_tsc(void *cpup)
 	local_irq_restore(flags);
 }
 
+static void kvm_do_sync_tsc(int cpu)
+{
+	spin_lock(&kvm_tsc_lock);
+	if (raw_smp_processor_id() != tsc_base_cpu) {
+		smp_call_function_single(tsc_base_cpu, kvm_sync_tsc,
+					 (void *)&cpu, 0);
+		smp_call_function_single(cpu, kvm_sync_tsc, (void *)&cpu, 1);
+	} else {
+		smp_call_function_single(cpu, kvm_sync_tsc, (void *)&cpu, 0);
+		smp_call_function_single(tsc_base_cpu, kvm_sync_tsc,
+					 (void *)&cpu, 1);
+	}
+	spin_unlock(&kvm_tsc_lock);
+}
+
 static void kvm_write_guest_time(struct kvm_vcpu *v)
 {
 	struct timespec ts;
@@ -1634,12 +1650,7 @@ out:
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	kvm_x86_ops->vcpu_load(vcpu, cpu);
-	if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) {
-		unsigned long khz = cpufreq_quick_get(cpu);
-		if (!khz)
-			khz = tsc_khz;
-		per_cpu(cpu_tsc_khz, cpu) = khz;
-	}
+	BUG_ON(per_cpu(cpu_tsc_khz, cpu) == 0);
 	kvm_request_guest_time_update(vcpu);
 }
 
@@ -3505,6 +3516,18 @@ static int kvm_x86_cpu_hotplug(struct notifier_block *notifier,
 
 	val &= ~CPU_TASKS_FROZEN;
 	switch (val) {
+	case CPU_DOWN_PREPARE:
+		if (cpu == tsc_base_cpu) {
+			int new_cpu;
+			spin_lock(&kvm_tsc_lock);
+			for_each_online_cpu(new_cpu)
+				if (new_cpu != tsc_base_cpu)
+					break;
+			tsc_base_cpu = new_cpu;
+			spin_unlock(&kvm_tsc_lock);
+		}
+		break;
+
 	case CPU_DYING:
 	case CPU_UP_CANCELED:
 		if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
@@ -3514,6 +3537,7 @@ static int kvm_x86_cpu_hotplug(struct notifier_block *notifier,
 	case CPU_ONLINE:
 		if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
 			per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
+		kvm_do_sync_tsc(cpu);
 		break;
 	}
 	return NOTIFY_OK;
@@ -3548,11 +3572,8 @@ static void kvm_timer_init(void)
 	per_cpu(cpu_tsc_shift, tsc_base_cpu) = 0;
 	per_cpu(cpu_tsc_offset, tsc_base_cpu) = 0;
 	for_each_online_cpu(cpu)
-		if (cpu != tsc_base_cpu) {
-			smp_call_function_single(cpu, kvm_sync_tsc,
-						 (void *)&cpu, 0);
-			kvm_sync_tsc((void *)&cpu);
-		}
+		if (cpu != tsc_base_cpu)
+			kvm_do_sync_tsc(cpu);
 	put_cpu();
 }
 
-- 
1.6.5.2

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