KVM: fast-path msi injection with irqfd
Store irq routing table pointer in the irqfd object,
and use that to inject MSI directly without bouncing out to
a kernel thread.
While we touch this structure, rearrange irqfd fields to make fastpath
better packed for better cache utilization.
This also adds some comments about locking rules and rcu usage in code.
Some notes on the design:
- Use pointer into the rt instead of copying an entry,
to make it possible to use rcu, thus side-stepping
locking complexities. We also save some memory this way.
- Old workqueue code is still used for level irqs.
I don't think we DTRT with level anyway, however,
it seems easier to keep the code around as
it has been thought through and debugged, and fix level later than
rip out and re-instate it later.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 8edca91..9f614b4 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -114,8 +114,8 @@
return r;
}
-static int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
- struct kvm *kvm, int irq_source_id, int level)
+int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
+ struct kvm *kvm, int irq_source_id, int level)
{
struct kvm_lapic_irq irq;
@@ -409,8 +409,9 @@
mutex_lock(&kvm->irq_lock);
old = kvm->irq_routing;
- rcu_assign_pointer(kvm->irq_routing, new);
+ kvm_irq_routing_update(kvm, new);
mutex_unlock(&kvm->irq_lock);
+
synchronize_rcu();
new = old;