Re: [dpdk-dev] [PATCH v3] vhost: allocate and free packets in bulk

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

On Fri, Apr 16, 2021 at 10:18 AM Balazs Nemeth <bnemeth@redhat.com> wrote:
>
> Move allocation out further and perform all allocation in bulk. The same
> goes for freeing packets. In the process, also rename
> virtio_dev_pktmbuf_alloc to virtio_dev_pktmbuf_prep. This
> function now receives an already allocated mbuf pointer.
>
> Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>

The title should indicate we are only touching the tx packed path.

What about tx split?
If it is too complex to rework, this can wait.


> ---
>  lib/librte_vhost/virtio_net.c | 58 +++++++++++++++++++++++------------
>  1 file changed, 38 insertions(+), 20 deletions(-)
>
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index ff39878609..d6d5636e0f 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -2168,6 +2168,24 @@ virtio_dev_pktmbuf_alloc(struct virtio_net *dev, struct rte_mempool *mp,
>         return NULL;
>  }
>
> +static __rte_always_inline int
> +virtio_dev_pktmbuf_prep(struct virtio_net *dev, struct rte_mbuf *pkt,
> +                        uint32_t data_len)
> +{
> +       if (rte_pktmbuf_tailroom(pkt) >= data_len)
> +               return 0;
> +
> +       /* attach an external buffer if supported */
> +       if (dev->extbuf && !virtio_dev_extbuf_alloc(pkt, data_len))
> +               return 0;
> +
> +       /* check if chained buffers are allowed */
> +       if (!dev->linearbuf)
> +               return 0;
> +
> +       return -1;
> +}
> +

If virtio_dev_pktmbuf_alloc() uses this new helper, we avoid
duplicating the logic.


>  static __rte_noinline uint16_t
>  virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>         struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count)

[snip]

> @@ -2429,7 +2440,7 @@ static __rte_always_inline int
>  virtio_dev_tx_single_packed(struct virtio_net *dev,
>                             struct vhost_virtqueue *vq,
>                             struct rte_mempool *mbuf_pool,
> -                           struct rte_mbuf **pkts)
> +                           struct rte_mbuf *pkts)
>  {
>
>         uint16_t buf_id, desc_count = 0;
> @@ -2462,26 +2473,33 @@ virtio_dev_tx_packed(struct virtio_net *dev,
>         uint32_t pkt_idx = 0;
>         uint32_t remained = count;
>
> +       if (rte_pktmbuf_alloc_bulk(mbuf_pool, pkts, count))
> +               return 0;
> +
>         do {
>                 rte_prefetch0(&vq->desc_packed[vq->last_avail_idx]);
>
>                 if (remained >= PACKED_BATCH_SIZE) {
> -                       if (!virtio_dev_tx_batch_packed(dev, vq, mbuf_pool,
> +                       if (!virtio_dev_tx_batch_packed(dev, vq,
>                                                         &pkts[pkt_idx])) {
>                                 pkt_idx += PACKED_BATCH_SIZE;
>                                 remained -= PACKED_BATCH_SIZE;
> +

No need for the extra line.


>                                 continue;
>                         }
>                 }
>
>                 if (virtio_dev_tx_single_packed(dev, vq, mbuf_pool,
> -                                               &pkts[pkt_idx]))
> +                                               pkts[pkt_idx]))
>                         break;
>                 pkt_idx++;
>                 remained--;
>
>         } while (remained);
>
> +       if (pkt_idx != count)
> +               rte_pktmbuf_free_bulk(&pkts[pkt_idx], count - pkt_idx);
> +
>         if (vq->shadow_used_idx) {
>                 do_data_copy_dequeue(vq);
>

With those comments addressed,
Reviewed-by: David Marchand <david.marchand@redhat.com>

Thanks Balazs!


-- 
David Marchand