netdev - Re: [PATCH net-next v2 13/14] virtio

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Message-ID: <CACGkMEtubJ8ND01J+Arpa4TB5kfdap7t6f9D5qc7-XkeFZYRKQ@mail.gmail.com>
Date:   Thu, 20 Apr 2023 14:32:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v2 13/14] virtio_net: small: optimize code

On Tue, Apr 18, 2023 at 2:53 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Avoid the problem that some variables(headroom and so on) will repeat
> the calculation when process xdp.

While at it, if we agree to use separate code paths for building skbs.

It would be better to have a helper for building skb for non XDP
cases, then we can hide those calculation there.

Thanks

>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index f6f5903face2..5a5636178bd3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1040,11 +1040,10 @@ static struct sk_buff *receive_small(struct net_device *dev,
>         struct sk_buff *skb;
>         struct bpf_prog *xdp_prog;
>         unsigned int xdp_headroom = (unsigned long)ctx;
> -       unsigned int header_offset = VIRTNET_RX_PAD + xdp_headroom;
> -       unsigned int headroom = vi->hdr_len + header_offset;
> -       unsigned int buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
> -                             SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>         struct page *page = virt_to_head_page(buf);
> +       unsigned int header_offset;
> +       unsigned int headroom;
> +       unsigned int buflen;
>
>         len -= vi->hdr_len;
>         stats->bytes += len;
> @@ -1072,6 +1071,11 @@ static struct sk_buff *receive_small(struct net_device *dev,
>         rcu_read_unlock();
>
>  skip_xdp:
> +       header_offset = VIRTNET_RX_PAD + xdp_headroom;
> +       headroom = vi->hdr_len + header_offset;
> +       buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
> +               SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +
>         skb = build_skb(buf, buflen);
>         if (!skb)
>                 goto err;
> --
> 2.32.0.3.g01195cf9f
>