From 039253166a57ee660dd2fbe92ca77fa65154751c Mon Sep 17 00:00:00 2001
Message-Id: <039253166a57ee660dd2fbe92ca77fa65154751c.1577105865.git.echaudro@redhat.com>
From: Eelco Chaudron <echaudro@redhat.com>
Date: Wed, 28 Aug 2019 10:49:39 -0400
Subject: [PATCH] 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>
---
 lib/librte_vhost/rte_vhost.h | 10 +++++++++-
 lib/librte_vhost/vhost.h     | 15 ++++++++++++---
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index 7fb1729..878e339 100644
--- 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
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -543,13 +543,19 @@ void *vhost_alloc_copy_ind_table(struct virtio_net *dev,
 
 		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 @@ void *vhost_alloc_copy_ind_table(struct virtio_net *dev,
 	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
-- 
1.8.3.1