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

On Thu, 30 Mar 2023 12:18:15 +0200, Paolo Abeni [off-list ref] wrote:

Hi,

On Tue, 2023-03-28 at 20:04 +0800, Xuan Zhuo wrote:

quoted

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