Re: [dpdk-dev] [PATCH v1 1/2] net/virtio: restrict pointer aliasing for NEON vpmd

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 6/11/20 5:32 AM, Joyce Kong wrote:
> Restrict pointer aliasing to allow the compiler to vectorize loops
> more aggressively.
> 
> With this patch, a 9.6% improvement is observed in throughput for
> the virtio-net PVP case, and a 2.4% perf improvement in throughput
> for the virtio-user PVP case. All performance data are measured
> under the 0.001% acceptable packet loss with 2 cores on the vhost
> 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 | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Very nice, we should consider doing the same on other platforms.

> diff --git a/drivers/net/virtio/virtio_rxtx_simple_neon.c b/drivers/net/virtio/virtio_rxtx_simple_neon.c
> index 363e2b330..c08dd51fb 100644
> --- a/drivers/net/virtio/virtio_rxtx_simple_neon.c
> +++ b/drivers/net/virtio/virtio_rxtx_simple_neon.c
> @@ -36,8 +36,8 @@
>   * - nb_pkts < RTE_VIRTIO_DESC_PER_LOOP, just return no packet
>   */
>  uint16_t
> -virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
> -	uint16_t nb_pkts)
> +virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf
> +		**__restrict rx_pkts, uint16_t nb_pkts)

Is __restrict supported by all the compilers?
Wouldn't it be better to introduce a wrapper?

>  {
>  	struct virtnet_rx *rxvq = rx_queue;
>  	struct virtqueue *vq = rxvq->vq;
>