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

Zachary Amsden
2009-12-15T04:12:17Z

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@redhat.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