[v2,3/6] lib/vhost: restrict pointer aliasing for packed vpmd

  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(-)
  

On Mon, Jul 6, 2020 at 9:50 AM Joyce Kong <joyce.kong@arm.com> wrote:
>
> 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;

For the neon bits, I trust you.


> 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;

But for the generic part, I'd like to get others opinion.
Added Zhihong and Adrian.


> @@ -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
>