[dpdk-dev] [PATCH v4 26/26] virtio: Fix updating vring descriptor index issue

[Ouyang Changchun]

Updating the vring descriptor index should be done before notifying host;
Remove 2 duplicated store memory barriers in both Rx and Tx path because there is
store memory barrier in vq_update_avail_idx function;
Notify the host only if packets actually transmitted(nb_tx > 0).

Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
---
 lib/librte_pmd_virtio/virtio_rxtx.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/lib/librte_pmd_virtio/virtio_rxtx.c b/lib/librte_pmd_virtio/virtio_rxtx.c
index 0225cc9..1d74b34 100644
--- a/lib/librte_pmd_virtio/virtio_rxtx.c
+++ b/lib/librte_pmd_virtio/virtio_rxtx.c
@@ -555,15 +555,14 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
 	}
 
 	if (likely(nb_enqueued)) {
-		virtio_wmb();
+		vq_update_avail_idx(rxvq);
+
 		if (unlikely(virtqueue_kick_prepare(rxvq))) {
 			virtqueue_notify(rxvq);
 			PMD_RX_LOG(DEBUG, "Notified\n");
 		}
 	}
 
-	vq_update_avail_idx(rxvq);
-
 	return nb_rx;
 }
 
@@ -719,14 +718,14 @@ virtio_recv_mergeable_pkts(void *rx_queue,
 	}
 
 	if (likely(nb_enqueued)) {
+		vq_update_avail_idx(rxvq);
+
 		if (unlikely(virtqueue_kick_prepare(rxvq))) {
 			virtqueue_notify(rxvq);
 			PMD_RX_LOG(DEBUG, "Notified");
 		}
 	}
 
-	vq_update_avail_idx(rxvq);
-
 	return nb_rx;
 }
 
@@ -800,14 +799,16 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 			break;
 		}
 	}
-	vq_update_avail_idx(txvq);
-	virtio_wmb();
 
 	txvq->packets += nb_tx;
 
-	if (unlikely(virtqueue_kick_prepare(txvq))) {
-		virtqueue_notify(txvq);
-		PMD_TX_LOG(DEBUG, "Notified backend after xmit");
+	if (likely(nb_tx)) {
+		vq_update_avail_idx(txvq);
+
+		if (unlikely(virtqueue_kick_prepare(txvq))) {
+			virtqueue_notify(txvq);
+			PMD_TX_LOG(DEBUG, "Notified backend after xmit");
+		}
 	}
 
 	return nb_tx;
-- 
1.8.4.2