Re: [PATCH net-next 7/8] virtio_net: introduce receive_mergeable_xdp()

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Thu, 30 Mar 2023 12:18:15 +0200, Paolo Abeni <pabeni@redhat.com> wrote:
> Hi,
>
> On Tue, 2023-03-28 at 20:04 +0800, Xuan Zhuo wrote:
> > The purpose of this patch is to simplify the receive_mergeable().
> > Separate all the logic of XDP into a function.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 128 +++++++++++++++++++++++----------------
> >  1 file changed, 76 insertions(+), 52 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 136131a7868a..c8978d8d8adb 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1316,6 +1316,63 @@ static void *mergeable_xdp_prepare(struct virtnet_info *vi,
> >  	return page_address(xdp_page) + VIRTIO_XDP_HEADROOM;
> >  }
> >
> > +static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> > +					     struct virtnet_info *vi,
> > +					     struct receive_queue *rq,
> > +					     struct bpf_prog *xdp_prog,
> > +					     void *buf,
> > +					     void *ctx,
> > +					     unsigned int len,
> > +					     unsigned int *xdp_xmit,
> > +					     struct virtnet_rq_stats *stats)
> > +{
> > +	struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> > +	int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> > +	struct page *page = virt_to_head_page(buf);
> > +	int offset = buf - page_address(page);
> > +	unsigned int xdp_frags_truesz = 0;
> > +	struct sk_buff *head_skb;
> > +	unsigned int frame_sz;
> > +	struct xdp_buff xdp;
> > +	void *data;
> > +	u32 act;
> > +	int err;
> > +
> > +	data = mergeable_xdp_prepare(vi, rq, xdp_prog, ctx, &frame_sz, &num_buf, &page,
> > +				     offset, &len, hdr);
> > +	if (!data)
> > +		goto err_xdp;
> > +
> > +	err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> > +					 &num_buf, &xdp_frags_truesz, stats);
> > +	if (unlikely(err))
> > +		goto err_xdp;
> > +
> > +	act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > +
> > +	switch (act) {
> > +	case VIRTNET_XDP_RES_PASS:
> > +		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> > +		if (unlikely(!head_skb))
> > +			goto err_xdp;
> > +		return head_skb;
> > +
> > +	case VIRTNET_XDP_RES_CONSUMED:
> > +		return NULL;
> > +
> > +	case VIRTNET_XDP_RES_DROP:
> > +		break;
> > +	}
> > +
> > +err_xdp:
> > +	put_page(page);
> > +	mergeable_buf_free(rq, num_buf, dev, stats);
> > +
> > +	stats->xdp_drops++;
> > +	stats->drops++;
> > +	return NULL;
> > +}
> > +
> >  static struct sk_buff *receive_mergeable(struct net_device *dev,
> >  					 struct virtnet_info *vi,
> >  					 struct receive_queue *rq,
> > @@ -1325,21 +1382,22 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >  					 unsigned int *xdp_xmit,
> >  					 struct virtnet_rq_stats *stats)
> >  {
> > -	struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> > -	int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> > -	struct page *page = virt_to_head_page(buf);
> > -	int offset = buf - page_address(page);
> > -	struct sk_buff *head_skb, *curr_skb;
> > -	struct bpf_prog *xdp_prog;
> >  	unsigned int truesize = mergeable_ctx_to_truesize(ctx);
> >  	unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> >  	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> >  	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> > -	unsigned int frame_sz;
> > -	int err;
> > +	struct virtio_net_hdr_mrg_rxbuf *hdr;
> > +	struct sk_buff *head_skb, *curr_skb;
> > +	struct bpf_prog *xdp_prog;
> > +	struct page *page;
> > +	int num_buf;
> > +	int offset;
> >
> >  	head_skb = NULL;
> >  	stats->bytes += len - vi->hdr_len;
> > +	hdr = buf;
> > +	num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> > +	page = virt_to_head_page(buf);
> >
> >  	if (unlikely(len > truesize - room)) {
> >  		pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> > @@ -1348,51 +1406,21 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >  		goto err_skb;
> >  	}
> >
> > -	if (likely(!vi->xdp_enabled)) {
> > -		xdp_prog = NULL;
> > -		goto skip_xdp;
> > -	}
> > -
> > -	rcu_read_lock();
> > -	xdp_prog = rcu_dereference(rq->xdp_prog);
> > -	if (xdp_prog) {
> > -		unsigned int xdp_frags_truesz = 0;
> > -		struct xdp_buff xdp;
> > -		void *data;
> > -		u32 act;
> > -
> > -		data = mergeable_xdp_prepare(vi, rq, xdp_prog, ctx, &frame_sz, &num_buf, &page,
> > -					     offset, &len, hdr);
> > -		if (!data)
> > -			goto err_xdp;
> > -
> > -		err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> > -						 &num_buf, &xdp_frags_truesz, stats);
> > -		if (unlikely(err))
> > -			goto err_xdp;
> > -
> > -		act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > -
> > -		switch (act) {
> > -		case VIRTNET_XDP_RES_PASS:
> > -			head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> > -			if (unlikely(!head_skb))
> > -				goto err_xdp;
> > -
> > +	if (likely(vi->xdp_enabled)) {
>
> This changes the branch prediction hint compared to the existing code;
> as we currently have:
> 	if (likely(!vi->xdp_enabled)) {
>
>
> and I think it would be better avoid such change.


Yes.

Will fix.

Thanks.


>
> Thanks,
>
> Paolo
>