netdev - Re: [PATCH net-next v6 09/10] virtio_net: xsk: rx: support recv merge mode

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Date: Fri, 28 Jun 2024 13:50:37 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>,
 Eugenio Pérez <eperezma@...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.dev,
 bpf@...r.kernel.org
Subject: Re: [PATCH net-next v6 09/10] virtio_net: xsk: rx: support recv merge mode

On Fri, 28 Jun 2024 10:19:44 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, Jun 18, 2024 at 3:57 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > Support AF-XDP for merge mode.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 139 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 139 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 06608d696e2e..cfa106aa8039 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -504,6 +504,10 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> >                                struct net_device *dev,
> >                                unsigned int *xdp_xmit,
> >                                struct virtnet_rq_stats *stats);
> > +static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > +                                              struct sk_buff *curr_skb,
> > +                                              struct page *page, void *buf,
> > +                                              int len, int truesize);
> >
> >  static bool is_xdp_frame(void *ptr)
> >  {
> > @@ -1128,6 +1132,139 @@ static struct sk_buff *virtnet_receive_xsk_small(struct net_device *dev, struct
> >         }
> >  }
> >
> > +static void xsk_drop_follow_bufs(struct net_device *dev,
> > +                                struct receive_queue *rq,
> > +                                u32 num_buf,
> > +                                struct virtnet_rq_stats *stats)
> > +{
> > +       struct xdp_buff *xdp;
> > +       u32 len;
> > +
> > +       while (num_buf-- > 1) {
> > +               xdp = virtqueue_get_buf(rq->vq, &len);
> > +               if (unlikely(!xdp)) {
> > +                       pr_debug("%s: rx error: %d buffers missing\n",
> > +                                dev->name, num_buf);
> > +                       DEV_STATS_INC(dev, rx_length_errors);
> > +                       break;
> > +               }
> > +               u64_stats_add(&stats->bytes, len);
> > +               xsk_buff_free(xdp);
> > +       }
> > +}
> > +
> > +static int xsk_append_merge_buffer(struct virtnet_info *vi,
> > +                                  struct receive_queue *rq,
> > +                                  struct sk_buff *head_skb,
> > +                                  u32 num_buf,
> > +                                  struct virtio_net_hdr_mrg_rxbuf *hdr,
> > +                                  struct virtnet_rq_stats *stats)
> > +{
> > +       struct sk_buff *curr_skb;
> > +       struct xdp_buff *xdp;
> > +       u32 len, truesize;
> > +       struct page *page;
> > +       void *buf;
> > +
> > +       curr_skb = head_skb;
> > +
> > +       while (--num_buf) {
> > +               buf = virtqueue_get_buf(rq->vq, &len);
> > +               if (unlikely(!buf)) {
> > +                       pr_debug("%s: rx error: %d buffers out of %d missing\n",
> > +                                vi->dev->name, num_buf,
> > +                                virtio16_to_cpu(vi->vdev,
> > +                                                hdr->num_buffers));
> > +                       DEV_STATS_INC(vi->dev, rx_length_errors);
> > +                       return -EINVAL;
> > +               }
> > +
> > +               u64_stats_add(&stats->bytes, len);
> > +
> > +               xdp = buf_to_xdp(vi, rq, buf, len);
> > +               if (!xdp)
> > +                       goto err;
> > +
> > +               buf = napi_alloc_frag(len);
>
> So we don't do this for non xsk paths. Any reason we can't reuse the
> existing codes?

Do you mean this code:

	while (--num_buf) {
		int num_skb_frags;

->		buf = virtnet_rq_get_buf(rq, &len, &ctx);
		if (unlikely(!buf)) {
			pr_debug("%s: rx error: %d buffers out of %d missing\n",
				 dev->name, num_buf,
				 virtio16_to_cpu(vi->vdev,
						 hdr->num_buffers));
			DEV_STATS_INC(dev, rx_length_errors);
			goto err_buf;
		}

		u64_stats_add(&stats->bytes, len);
		page = virt_to_head_page(buf);

->		truesize = mergeable_ctx_to_truesize(ctx);
->		headroom = mergeable_ctx_to_headroom(ctx);
->		tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
->		room = SKB_DATA_ALIGN(headroom + tailroom);
->		if (unlikely(len > truesize - room)) {
->			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
->				 dev->name, len, (unsigned long)(truesize - room));
->			DEV_STATS_INC(dev, rx_length_errors);
->			goto err_skb;
->		}

		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
						    buf, len, truesize);
		if (!curr_skb)
			goto err_skb;
	}

The code lines that are marked are differ.

The same logic is separated to function virtnet_skb_append_frag().

So the code is similitude, but we can not merge them.

Thanks.



>
> Thanks
>