netdev - Re: [PATCH net-next v4 12/15] virtio_net: small: avoid double counting in xdp scenarios

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Date:   Fri, 28 Apr 2023 09:54:16 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...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 v4 12/15] virtio_net: small: avoid double counting in xdp scenarios

On Thu, 27 Apr 2023 21:08:25 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Thu, Apr 27, 2023 at 11:05:31AM +0800, Xuan Zhuo wrote:
> > Avoid the problem that some variables(headroom and so on) will repeat
> > the calculation when process xdp.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > Acked-by: Jason Wang <jasowang@...hat.com>
>
>
> this is "code duplication" not "double counting".

Will fix.

Thanks.


>
>
> > ---
> >  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 b8ec642899c9..f832ab8a3e6e 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1027,11 +1027,10 @@ 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;
> > @@ -1059,6 +1058,11 @@ 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
>