kvm: Record the preemption status of vcpus using preempt notifiers

Note that we mark as preempted only when vcpu's task state was Running during preemption. Thanks Jiannan, Avi for preemption notifier ideas. Thanks Gleb, PeterZ for their precious suggestions. Thanks Srikar for an idea on avoiding rcu lock while checking task state that improved overcommit numbers. Reviewed-by: Chegu Vinod <[email protected]> Reviewed-by: Marcelo Tosatti <[email protected]> Signed-off-by: Raghavendra K T <[email protected]> Signed-off-by: Gleb Natapov <[email protected]>
ambv · Mar 11, 2013 · 3a08a8f · 3a08a8f
1 parent 5da5960
commit 3a08a8f
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diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
@@ -253,6 +253,7 @@ struct kvm_vcpu {
 		bool dy_eligible;
 	} spin_loop;
 #endif
+	bool preempted;
 	struct kvm_vcpu_arch arch;
 };
 

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -244,6 +244,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 
 	kvm_vcpu_set_in_spin_loop(vcpu, false);
 	kvm_vcpu_set_dy_eligible(vcpu, false);
+	vcpu->preempted = false;
 
 	r = kvm_arch_vcpu_init(vcpu);
 	if (r < 0)
@@ -2880,6 +2881,8 @@ struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)
 static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
 {
 	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
+	if (vcpu->preempted)
+		vcpu->preempted = false;
 
 	kvm_arch_vcpu_load(vcpu, cpu);
 }
@@ -2889,6 +2892,8 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 {
 	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
 
+	if (current->state == TASK_RUNNING)
+		vcpu->preempted = true;
 	kvm_arch_vcpu_put(vcpu);
 }