Re: [PATCH v2 4/4] vhost: improve RARP handling in dequeue paths

[David Marchand <david.marchand@redhat.com>]

On Wed, Jan 15, 2025 at 1:59 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> With previous refactoring, we can now simplify the RARP
> packet injection handling in both the sync and async
> dequeue paths.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/vhost/virtio_net.c | 42 ++++++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 24 deletions(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 59ea2d16a5..fab45ebd54 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -3662,21 +3662,23 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>                  * learning table will get updated first.
>                  */
>                 pkts[0] = rarp_mbuf;

Well, ideally it would be pkts[nb_rx], but see comment below.

> -               vhost_queue_stats_update(dev, vq, pkts, 1);
> -               pkts++;
> -               count -= 1;
> +               nb_rx += 1;
>         }

With this change, the rarp_mbuf variable is unneeded.
You can store to pkts[nb_rx] when calling rte_net_make_rarp_packet()
(and at the same time, move the comment about injecting the packet to
the head of the array).



>
>         if (vq_is_packed(dev)) {
>                 if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
> -                       nb_rx = virtio_dev_tx_packed_legacy(dev, vq, mbuf_pool, pkts, count);
> +                       nb_rx += virtio_dev_tx_packed_legacy(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx);
>                 else
> -                       nb_rx = virtio_dev_tx_packed_compliant(dev, vq, mbuf_pool, pkts, count);
> +                       nb_rx += virtio_dev_tx_packed_compliant(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx);
>         } else {
>                 if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
> -                       nb_rx = virtio_dev_tx_split_legacy(dev, vq, mbuf_pool, pkts, count);
> +                       nb_rx += virtio_dev_tx_split_legacy(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx);
>                 else
> -                       nb_rx = virtio_dev_tx_split_compliant(dev, vq, mbuf_pool, pkts, count);
> +                       nb_rx += virtio_dev_tx_split_compliant(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx);
>         }
>
>         vhost_queue_stats_update(dev, vq, pkts, nb_rx);
> @@ -3687,9 +3689,6 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>  out_access_unlock:
>         rte_rwlock_read_unlock(&vq->access_lock);
>
> -       if (unlikely(rarp_mbuf != NULL))
> -               nb_rx += 1;
> -
>  out_no_unlock:
>         return nb_rx;
>  }
> @@ -4285,25 +4284,23 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>                  * learning table will get updated first.
>                  */
>                 pkts[0] = rarp_mbuf;
> -               vhost_queue_stats_update(dev, vq, pkts, 1);
> -               pkts++;
> -               count -= 1;
> +               nb_rx += 1;
>         }

Idem.

>
>         if (vq_is_packed(dev)) {
>                 if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
> -                       nb_rx = virtio_dev_tx_async_packed_legacy(dev, vq, mbuf_pool,
> -                                       pkts, count, dma_id, vchan_id);
> +                       nb_rx += virtio_dev_tx_async_packed_legacy(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>                 else
> -                       nb_rx = virtio_dev_tx_async_packed_compliant(dev, vq, mbuf_pool,
> -                                       pkts, count, dma_id, vchan_id);
> +                       nb_rx += virtio_dev_tx_async_packed_compliant(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>         } else {
>                 if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
> -                       nb_rx = virtio_dev_tx_async_split_legacy(dev, vq, mbuf_pool,
> -                                       pkts, count, dma_id, vchan_id);
> +                       nb_rx += virtio_dev_tx_async_split_legacy(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>                 else
> -                       nb_rx = virtio_dev_tx_async_split_compliant(dev, vq, mbuf_pool,
> -                                       pkts, count, dma_id, vchan_id);
> +                       nb_rx += virtio_dev_tx_async_split_compliant(dev, vq, mbuf_pool,
> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>         }
>
>         *nr_inflight = vq->async->pkts_inflight_n;
> @@ -4315,9 +4312,6 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>  out_access_unlock:
>         rte_rwlock_read_unlock(&vq->access_lock);
>
> -       if (unlikely(rarp_mbuf != NULL))
> -               nb_rx += 1;
> -
>  out_no_unlock:
>         return nb_rx;
>  }
> --
> 2.47.1
>


-- 
David Marchand