[dpdk-dev] [PATCH v2 3/6] lib/vhost: restrict pointer aliasing for packed vpmd

[Joyce Kong <joyce.kong@arm.com>]

Restrict pointer aliasing to allow the compiler to vectorize loop
more aggressively.

With this patch, a 9.6% improvement is observed in throughput for
the packed virtio-net PVP case, and a 2.8% improvement in throughput
for the packed virtio-user PVP case. All performance data are measured
under 0.001% acceptable packet loss with 1 core on both vhost and
virtio side.

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
---
 drivers/net/virtio/virtio_rxtx_simple_neon.c |  5 +++--
 lib/librte_vhost/virtio_net.c                | 14 +++++++-------
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx_simple_neon.c b/drivers/net/virtio/virtio_rxtx_simple_neon.c
index 5febfb0f5..31824a931 100644
--- a/drivers/net/virtio/virtio_rxtx_simple_neon.c
+++ b/drivers/net/virtio/virtio_rxtx_simple_neon.c
@@ -36,8 +36,9 @@
  * - nb_pkts < RTE_VIRTIO_DESC_PER_LOOP, just return no packet
  */
 uint16_t
-virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf
-		**__rte_restrict rx_pkts, uint16_t nb_pkts)
+virtio_recv_pkts_vec(void *rx_queue,
+		struct rte_mbuf **__rte_restrict rx_pkts,
+		uint16_t nb_pkts)
 {
 	struct virtnet_rx *rxvq = rx_queue;
 	struct virtqueue *vq = rxvq->vq;
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 751c1f373..e60358251 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1133,8 +1133,8 @@ virtio_dev_rx_single_packed(struct virtio_net *dev,
 
 static __rte_noinline uint32_t
 virtio_dev_rx_packed(struct virtio_net *dev,
-		     struct vhost_virtqueue *vq,
-		     struct rte_mbuf **pkts,
+		     struct vhost_virtqueue *__rte_restrict vq,
+		     struct rte_mbuf **__rte_restrict pkts,
 		     uint32_t count)
 {
 	uint32_t pkt_idx = 0;
@@ -1219,7 +1219,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 
 uint16_t
 rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
-	struct rte_mbuf **pkts, uint16_t count)
+	struct rte_mbuf **__rte_restrict pkts, uint16_t count)
 {
 	struct virtio_net *dev = get_device(vid);
 
@@ -2124,9 +2124,9 @@ free_zmbuf(struct vhost_virtqueue *vq)
 
 static __rte_noinline uint16_t
 virtio_dev_tx_packed_zmbuf(struct virtio_net *dev,
-			   struct vhost_virtqueue *vq,
+			   struct vhost_virtqueue *__rte_restrict vq,
 			   struct rte_mempool *mbuf_pool,
-			   struct rte_mbuf **pkts,
+			   struct rte_mbuf **__rte_restrict pkts,
 			   uint32_t count)
 {
 	uint32_t pkt_idx = 0;
@@ -2160,9 +2160,9 @@ virtio_dev_tx_packed_zmbuf(struct virtio_net *dev,
 
 static __rte_noinline uint16_t
 virtio_dev_tx_packed(struct virtio_net *dev,
-		     struct vhost_virtqueue *vq,
+		     struct vhost_virtqueue *__rte_restrict vq,
 		     struct rte_mempool *mbuf_pool,
-		     struct rte_mbuf **pkts,
+		     struct rte_mbuf **__rte_restrict pkts,
 		     uint32_t count)
 {
 	uint32_t pkt_idx = 0;
-- 
2.27.0