KVM: X86: trigger kvmclock sync request just once on VM creation

In the progress of vCPUs creation, it queues a kvmclock sync worker to the global
workqueue before each vCPU creation completes. The workqueue subsystem guarantees
not to queue the already queued work; however, we can make the logic more clear by
making just one leader to trigger this kvmclock sync request, and also save on
cacheline bouncing caused by test_and_set_bit.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5762c031b0c7e1cb725b69c46d3e00bd76baa8f..78e34c968ab54ae3190b9df669a79577535833be 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9335,11 +9335,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 
        mutex_unlock(&vcpu->mutex);
 
-       if (!kvmclock_periodic_sync)
-               return;
-
-       schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
-                                       KVMCLOCK_SYNC_PERIOD);
+       if (kvmclock_periodic_sync && vcpu->vcpu_idx == 0)
+               schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+                                               KVMCLOCK_SYNC_PERIOD);
 }
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)