KVM: VMX: Avoid unnecessary vcpu_load()/vcpu_put() cycles

By checking if a reschedule is needed, we avoid dropping the vcpu.

[With changes by me, based on Anthony Liguori's observations]
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm_main.c

@@ -1590,6 +1590,8 @@ static int set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
 
 void kvm_resched(struct kvm_vcpu *vcpu)
 {
+	if (!need_resched())
+		return;
 	vcpu_put(vcpu);
 	cond_resched();
 	vcpu_load(vcpu);