From: Ouyang Changchun <changchun.ouyang@intel.com>
Date: Mon, 9 Feb 2015 01:14:15 +0000 (+0800)
Subject: virtio: fix update of vring descriptor index
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=8c09c20fb4cde76e53d87bd50acf2b441ecf6eb8;p=dpdk.git

virtio: fix update of vring descriptor index

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@intel.com>
Acked-by: Huawei Xie <huawei.xie@intel.com>
---

diff --git a/lib/librte_pmd_virtio/virtio_rxtx.c b/lib/librte_pmd_virtio/virtio_rxtx.c
index 78af3347bf..1db1dd8d95 100644
--- a/lib/librte_pmd_virtio/virtio_rxtx.c
+++ b/lib/librte_pmd_virtio/virtio_rxtx.c
@@ -516,15 +516,14 @@ 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;
 }
 
@@ -668,14 +667,14 @@ 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;
 }
 
@@ -735,14 +734,16 @@ 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;