vhost: add device op when notification to guest is sent

This patch adds an operation callback which gets called every time
the library is waking up the guest trough an eventfd_write() call.

This can be used by 3rd party application, like OVS, to track the
number of times interrupts where generated. This might be of
interest to find out system-call were called in the fast path.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index 7fb1729..878e339 100644 (file)
--- a/lib/librte_vhost/rte_vhost.h
+++ b/lib/librte_vhost/rte_vhost.h
@@ -172,7 +172,15 @@ struct vhost_device_ops {
        int (*new_connection)(int vid);
        void (*destroy_connection)(int vid);
 
-       void *reserved[2]; /**< Reserved for future extension */
+       /**
+        * This callback gets called each time a guest gets notified
+        * about waiting packets. This is the interrupt handling trough
+        * the eventfd_write(callfd), which can be used for counting these
+        * "slow" syscalls.
+        */
+       void (*guest_notified)(int vid);
+
+       void *reserved[1]; /**< Reserved for future extension */
 };
 
 /**

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 884befa..5131a97 100644 (file)
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -543,13 +543,19 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 
                if ((vhost_need_event(vhost_used_event(vq), new, old) &&
                                        (vq->callfd >= 0)) ||
-                               unlikely(!signalled_used_valid))
+                               unlikely(!signalled_used_valid)) {
                        eventfd_write(vq->callfd, (eventfd_t) 1);
+                       if (dev->notify_ops->guest_notified)
+                               dev->notify_ops->guest_notified(dev->vid);
+               }
        } else {
                /* Kick the guest if necessary. */
                if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-                               && (vq->callfd >= 0))
+                               && (vq->callfd >= 0)) {
                        eventfd_write(vq->callfd, (eventfd_t)1);
+                       if (dev->notify_ops->guest_notified)
+                               dev->notify_ops->guest_notified(dev->vid);
+               }
        }
 }
 
@@ -600,8 +606,11 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
        if (vhost_need_event(off, new, old))
                kick = true;
 kick:
-       if (kick)
+       if (kick) {
                eventfd_write(vq->callfd, (eventfd_t)1);
+               if (dev->notify_ops->guest_notified)
+                       dev->notify_ops->guest_notified(dev->vid);
+       }
 }
 
 static __rte_always_inline void