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Date: Fri, 31 Mar 2023 15:18:17 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
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,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next 7/8] virtio_net: introduce receive_mergeable_xdp()
On Thu, 30 Mar 2023 12:18:15 +0200, Paolo Abeni <pabeni@...hat.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@...ux.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
>
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