[dpdk-dev] [PATCH] virtio_net: kick guest even when virtio queue is full

[Agota Benyhe <agota.benyhe@ericsson.com>]

From: Patrik Andersson R <patrik.r.andersson@ericsson.com>

Changing the vring call file descriptor during virtio device enqueue
operation may lead to "kick" on a file descriptor that is closed. As
a consequence the guest might not be notified of new packets in the
enqueue.

The suggested change will add some extra load on DPDK and on the
guest if the queue is frequently full. Any application using DPDK
should avoid attempting retransmissions when the zero packets are
enqueued.

To overcome this problem, the kick operation in virtio_dev_merge_rx()
was excluded from the pkt_idx > 0 condition. A similar change was
done in virtio_dev_rx().

Signed-off-by: Patrik Andersson R <patrik.r.andersson@ericsson.com>
Signed-off-by: Agota Benyhe <agota.benyhe@ericsson.com>
---
 lib/librte_vhost/virtio_net.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 6fee16e..f5fc8c0 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -59,6 +59,13 @@ is_valid_virt_queue_idx(uint32_t idx, int is_tx, uint32_t nr_vring)
 }
 
 static __rte_always_inline void
+kick_guest_if_necessary(const struct vhost_virtqueue *vq) {
+	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+			&& (vq->callfd >= 0))
+		eventfd_write(vq->callfd, (eventfd_t)1);
+}
+
+static __rte_always_inline void
 do_flush_shadow_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			  uint16_t to, uint16_t from, uint16_t size)
 {
@@ -344,8 +351,11 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 	free_entries = avail_idx - start_idx;
 	count = RTE_MIN(count, free_entries);
 	count = RTE_MIN(count, (uint32_t)MAX_PKT_BURST);
-	if (count == 0)
+
+	if (count == 0) {
+                kick_guest_if_necessary(vq);
 		goto out;
+        }
 
 	LOG_DEBUG(VHOST_DATA, "(%d) start_idx %d | end_idx %d\n",
 		dev->vid, start_idx, start_idx + count);
@@ -411,10 +421,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 	/* flush used->idx update before we read avail->flags. */
 	rte_mb();
 
-	/* Kick the guest if necessary. */
-	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-			&& (vq->callfd >= 0))
-		eventfd_write(vq->callfd, (eventfd_t)1);
+        kick_guest_if_necessary(vq);
 out:
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_unlock(vq);
@@ -704,13 +711,9 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
 
 		/* flush used->idx update before we read avail->flags. */
 		rte_mb();
-
-		/* Kick the guest if necessary. */
-		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-				&& (vq->callfd >= 0))
-			eventfd_write(vq->callfd, (eventfd_t)1);
 	}
 
+        kick_guest_if_necessary(vq);
 out:
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 		vhost_user_iotlb_rd_unlock(vq);
-- 
2.7.4