Re: [PATCH v7 2/2] net/af_xdp: Refactor af_xdp_tx_zc

[Maryam Tahhan <mtahhan@redhat.com>]

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On Sat 1 Feb 2025, 10:03 Ariel Otilibili, <ariel.otilibili@6wind.com> wrote:

> Both legs of the loop share the same logic: the common parts are about
> reserving and filling both address and length into the description.
>
> This is moved into reserve_and_fill().
>
> Bugzilla ID: 1440
> Suggested-by: Maryam Tahhan <mtahhan@redhat.com>
> Signed-off-by: Ariel Otilibili <ariel.otilibili@6wind.com>
> ---
>  drivers/net/af_xdp/rte_eth_af_xdp.c | 62 ++++++++++++++++-------------
>  1 file changed, 34 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
> b/drivers/net/af_xdp/rte_eth_af_xdp.c
> index 092bcb73aa0a..840a12dbf508 100644
> --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> @@ -536,6 +536,31 @@ kick_tx(struct pkt_tx_queue *txq, struct
> xsk_ring_cons *cq)
>                 }
>  }
>
> +static inline struct xdp_desc *
> +reserve_and_fill(struct pkt_tx_queue *txq, struct rte_mbuf *mbuf,
> +                struct xsk_umem_info *umem)
> +{
> +       struct xdp_desc *desc = NULL;
> +       uint32_t *idx_tx = NULL;
> +       uint64_t addr, offset;
> +
> +       if (!xsk_ring_prod__reserve(&txq->tx, 1, idx_tx))
> +               goto out;
> +
> +       desc = xsk_ring_prod__tx_desc(&txq->tx, *idx_tx);
> +       desc->len = mbuf->pkt_len;
> +
> +       addr = (uint64_t)mbuf - (uint64_t)umem->buffer
> +               - umem->mb_pool->header_size;
> +       offset = rte_pktmbuf_mtod(mbuf, uint64_t) - (uint64_t)mbuf
> +               + umem->mb_pool->header_size;
> +       offset = offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT;
> +       desc->addr = addr | offset;
> +
> +out:
> +       return desc;
> +}
> +
>  #if defined(XDP_UMEM_UNALIGNED_CHUNK_FLAG)
>  static uint16_t
>  af_xdp_tx_zc(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
> @@ -545,10 +570,8 @@ af_xdp_tx_zc(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>         struct rte_mbuf *mbuf;
>         unsigned long tx_bytes = 0;
>         int i;
> -       uint32_t idx_tx;
>         uint16_t count = 0;
>         struct xdp_desc *desc;
> -       uint64_t addr, offset;
>         struct xsk_ring_cons *cq = &txq->pair->cq;
>         uint32_t free_thresh = cq->size >> 1;
>
> @@ -559,21 +582,12 @@ af_xdp_tx_zc(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>                 mbuf = bufs[i];
>
>                 if (mbuf->pool == umem->mb_pool) {
> -                       if (!xsk_ring_prod__reserve(&txq->tx, 1, &idx_tx))
> {
> +                       if (!(desc = reserve_and_fill(txq, mbuf, umem))) {
>                                 kick_tx(txq, cq);
> -                               if (!xsk_ring_prod__reserve(&txq->tx, 1,
> -                                                           &idx_tx))
> +                               if (!(desc = reserve_and_fill(txq, mbuf,
> umem)))
>                                         goto out;
>                         }
> -                       desc = xsk_ring_prod__tx_desc(&txq->tx, idx_tx);
> -                       desc->len = mbuf->pkt_len;
> -                       addr = (uint64_t)mbuf - (uint64_t)umem->buffer -
> -                                       umem->mb_pool->header_size;
> -                       offset = rte_pktmbuf_mtod(mbuf, uint64_t) -
> -                                       (uint64_t)mbuf +
> -                                       umem->mb_pool->header_size;
> -                       offset = offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT;
> -                       desc->addr = addr | offset;
> +
>                         tx_bytes += desc->len;
>                         count++;
>                 } else {
> @@ -584,26 +598,18 @@ af_xdp_tx_zc(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>                         if (local_mbuf == NULL)
>                                 goto out;
>
> -                       if (!xsk_ring_prod__reserve(&txq->tx, 1, &idx_tx))
> {
> +                       if (!(desc = reserve_and_fill(txq, local_mbuf,
> umem))) {
>                                 rte_pktmbuf_free(local_mbuf);
>                                 goto out;
>                         }
>
> -                       desc = xsk_ring_prod__tx_desc(&txq->tx, idx_tx);
> -                       desc->len = mbuf->pkt_len;
> -
>

So I think i spotted one issue, you might need override desc->len after the
call to the reserve_and_fill function so as it's not taken supposed to be
from local_mbuf here.

-                       addr = (uint64_t)local_mbuf -
> (uint64_t)umem->buffer -
> -                                       umem->mb_pool->header_size;
> -                       offset = rte_pktmbuf_mtod(local_mbuf, uint64_t) -
> -                                       (uint64_t)local_mbuf +
> -                                       umem->mb_pool->header_size;
> -                       pkt = xsk_umem__get_data(umem->buffer, addr +
> offset);
> -                       offset = offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT;
> -                       desc->addr = addr | offset;
> +                       pkt = xsk_umem__get_data(umem->buffer,
> +                                                (desc->addr & ~0xFFF)
> +                                                + (desc->addr & 0xFFF));
>

Would prefer to move this pkt assignment to reserve_and_fill()
What if we passed a void **ppkt to reserve_and_fill()  then kept the
original logic just wrapped in a NULL check?

 if (ppkt) {
      *ppkt = xsk_umem__get_data(umem->buffer, addr + offset);
    }


Before the offset and desc->addr
    offset = offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT;
    desc->addr = addr | offset;

WDYT?

                        rte_memcpy(pkt, rte_pktmbuf_mtod(mbuf, void *),
> -                                       desc->len);
> -                       tx_bytes += desc->len;
> +                                  desc->len);
>                         rte_pktmbuf_free(mbuf);
> +                       tx_bytes += desc->len;
>                         count++;
>                 }
>         }
> --
> 2.30.2
>
>

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