Re: [dpdk-dev] [PATCH 4/4] net/mlx5: add multi-segment packets in MPRQ mode

[Slava Ovsiienko <viacheslavo@mellanox.com>]

> -----Original Message-----
> From: Alexander Kozyrev <akozyrev@mellanox.com>
> Sent: Wednesday, April 1, 2020 0:53
> To: dev@dpdk.org
> Cc: Raslan Darawsheh <rasland@mellanox.com>; Matan Azrad
> <matan@mellanox.com>; Slava Ovsiienko <viacheslavo@mellanox.com>;
> ferruh.yigit@intel.com; Thomas Monjalon <thomas@monjalon.net>
> Subject: [PATCH 4/4] net/mlx5: add multi-segment packets in MPRQ mode
> 
> The multi-stride operations now allow to reduce a stride size while supporting
> Jumbo frames. That means that it is possible to have mbufs configured with a
> size smaller than the whole packet received. It is not an issue during normal
> MPRQ operations since we attach external buffers instead of copying the data
> into the mbuf itself. But it is not the case in "emergency mode"
> when we have to copy every packet because of no more external mbufs are
> available. Assemble a multi-segment packet to overcome this issue in case
> scatter mode is enabled, drop a packet if not.
> 
> Signed-off-by: Alexander Kozyrev <akozyrev@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>

> ---
>  drivers/net/mlx5/mlx5_rxtx.c | 47
> ++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c index
> 4c27952..7ce3732 100644
> --- a/drivers/net/mlx5/mlx5_rxtx.c
> +++ b/drivers/net/mlx5/mlx5_rxtx.c
> @@ -1734,22 +1734,52 @@ enum mlx5_txcmp_code {
>  		 * Memcpy packets to the target mbuf if:
>  		 * - The size of packet is smaller than
> mprq_max_memcpy_len.
>  		 * - Out of buffer in the Mempool for Multi-Packet RQ.
> -		 * - There is no space for a headroom and scatter is disabled.
> +		 * - The packet's stride overlaps a headroom and scatter is off.
>  		 */
>  		if (len <= rxq->mprq_max_memcpy_len ||
>  		    rxq->mprq_repl == NULL ||
>  		    (hdrm_overlap > 0 && !rxq->strd_scatter_en)) {
> -			/*
> -			 * When memcpy'ing packet due to out-of-buffer, the
> -			 * packet must be smaller than the target mbuf.
> -			 */
> -			if (unlikely(rte_pktmbuf_tailroom(pkt) < len)) {
> +			if (likely(rte_pktmbuf_tailroom(pkt) >= len)) {
> +				rte_memcpy(rte_pktmbuf_mtod(pkt, void *),
> +					   addr, len);
> +				DATA_LEN(pkt) = len;
> +			} else if (rxq->strd_scatter_en) {
> +				struct rte_mbuf *prev = pkt;
> +				uint32_t seg_len =
> +					RTE_MIN(rte_pktmbuf_tailroom(pkt),
> len);
> +				uint32_t rem_len = len - seg_len;
> +
> +				rte_memcpy(rte_pktmbuf_mtod(pkt, void *),
> +					   addr, seg_len);
> +				DATA_LEN(pkt) = seg_len;
> +				while (rem_len) {
> +					struct rte_mbuf *next =
> +						rte_pktmbuf_alloc(rxq->mp);
> +
> +					if (unlikely(next == NULL)) {
> +						rte_pktmbuf_free(pkt);
> +						++rxq->stats.rx_nombuf;
> +						goto out;
> +					}
> +					NEXT(prev) = next;
> +					SET_DATA_OFF(next, 0);
> +					addr = RTE_PTR_ADD(addr, seg_len);
> +					seg_len = RTE_MIN
> +						(rte_pktmbuf_tailroom(next),
> +						 rem_len);
> +					rte_memcpy
> +						(rte_pktmbuf_mtod(next,
> void *),
> +						 addr, seg_len);
> +					DATA_LEN(next) = seg_len;
> +					rem_len -= seg_len;
> +					prev = next;
> +					++NB_SEGS(pkt);
> +				}
> +			} else {
>  				rte_pktmbuf_free_seg(pkt);
>  				++rxq->stats.idropped;
>  				continue;
>  			}
> -			rte_memcpy(rte_pktmbuf_mtod(pkt, void *), addr,
> len);
> -			DATA_LEN(pkt) = len;
>  		} else {
>  			rte_iova_t buf_iova;
>  			struct rte_mbuf_ext_shared_info *shinfo; @@ -
> 1826,6 +1856,7 @@ enum mlx5_txcmp_code {
>  		*(pkts++) = pkt;
>  		++i;
>  	}
> +out:
>  	/* Update the consumer indexes. */
>  	rxq->consumed_strd = consumed_strd;
>  	rte_cio_wmb();
> --
> 1.8.3.1