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SubjectRe: [PATCH net 6/9] virtio-net: make rx buf size estimation works for XDP
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On 16-12-23 06:37 AM, Jason Wang wrote:
> We don't update ewma rx buf size in the case of XDP. This will lead
> underestimation of rx buf size which causes host to produce more than
> one buffers. This will greatly increase the possibility of XDP page
> linearization.
>
> Cc: John Fastabend <john.r.fastabend@intel.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> drivers/net/virtio_net.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0778dc8..77ae358 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -584,10 +584,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> put_page(page);
> head_skb = page_to_skb(vi, rq, xdp_page,
> 0, len, PAGE_SIZE);
> + ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
> return head_skb;
> }
> break;
> case XDP_TX:
> + ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
> if (unlikely(xdp_page != page))
> goto err_xdp;
> rcu_read_unlock();
> @@ -596,6 +598,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> default:
> if (unlikely(xdp_page != page))
> __free_pages(xdp_page, 0);
> + ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
> goto err_xdp;
> }
> }
>

Looks needed although I guess it will only be the case with
MTU > ETH_DATA_LEN because of the clamp in get_mergeable_buf_len().
Although XDP setup allows MTU up to page_size - hdr so certainly
will happen with ~MTU > 1500.

I need to add some various MTU tests to my setup.

Acked-by: John Fastabend <john.r.fastabend@intel.com>

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