[dpdk-dev] [PATCH] ixgbe: prefetch packet headers in vector PMD receive function

[Zoltan Kiss]

Hi,

I just realized I've missed the "[PATCH]" tag from the subject. Did 
anyone had time to review this?

Regards,

Zoltan

On 01/09/15 20:17, Zoltan Kiss wrote:
> The lack of this prefetch causes a significant performance drop in
> OVS-DPDK: 13.3 Mpps instead of 14 when forwarding 64 byte packets. Even
> though OVS prefetches the next packet's header before it starts processing
> the current one, it doesn't get there fast enough. This aligns with the
> behaviour of other receive functions.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss at linaro.org>
> ---
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> index cf25a53..51299fa 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> @@ -502,6 +502,15 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
>                  _mm_storeu_si128((void *)&rx_pkts[pos]->rx_descriptor_fields1,
>                                  pkt_mb1);
>
> +               rte_packet_prefetch((char*)(rx_pkts[pos]->buf_addr) +
> +                                   RTE_PKTMBUF_HEADROOM);
> +               rte_packet_prefetch((char*)(rx_pkts[pos + 1]->buf_addr) +
> +                                   RTE_PKTMBUF_HEADROOM);
> +               rte_packet_prefetch((char*)(rx_pkts[pos + 2]->buf_addr) +
> +                                   RTE_PKTMBUF_HEADROOM);
> +               rte_packet_prefetch((char*)(rx_pkts[pos + 3]->buf_addr) +
> +                                   RTE_PKTMBUF_HEADROOM);
> +
>                  /* C.4 calc avaialbe number of desc */
>                  var = __builtin_popcountll(_mm_cvtsi128_si64(staterr));
>                  nb_pkts_recd += var;
>