Re: [PATCH net-next v5 08/15] virtio-net: split the receive_mergeable function

On Wed, 16 Jun 2021 15:33:05 +0800, Jason Wang [off-list ref] wrote:

在 2021/6/10 下午4:22, Xuan Zhuo 写道:

quoted

receive_mergeable() is too complicated, so this function is split here.
One is to make the function more readable. On the other hand, the two
independent functions will be called separately in subsequent patches.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
  drivers/net/virtio_net.c | 181 ++++++++++++++++++++++++---------------
  1 file changed, 111 insertions(+), 70 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3fd87bf2b2ad..989aba600e63 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -733,6 +733,109 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
  	return NULL;
  }

+static void merge_drop_follow_bufs(struct net_device *dev,
+				   struct receive_queue *rq,
+				   u16 num_buf,
+				   struct virtnet_rq_stats *stats)

Patch looks good. Nit here, I guess we need a better name, how about
"merge_buffers()" for this and "drop_buffers()" for the next function?

The name sounds good.

Thanks.

Thanks

quoted

+{
+	struct page *page;
+	unsigned int len;
+	void *buf;
+
+	while (num_buf-- > 1) {
+		buf = virtqueue_get_buf(rq->vq, &len);
+		if (unlikely(!buf)) {
+			pr_debug("%s: rx error: %d buffers missing\n",
+				 dev->name, num_buf);
+			dev->stats.rx_length_errors++;
+			break;
+		}
+		stats->bytes += len;
+		page = virt_to_head_page(buf);
+		put_page(page);
+	}
+}
+
+static struct sk_buff *merge_receive_follow_bufs(struct net_device *dev,
+						 struct virtnet_info *vi,
+						 struct receive_queue *rq,
+						 struct sk_buff *head_skb,
+						 u16 num_buf,
+						 struct virtnet_rq_stats *stats)
+{
+	struct sk_buff *curr_skb;
+	unsigned int truesize;
+	unsigned int len, num;
+	struct page *page;
+	void *buf, *ctx;
+	int offset;
+
+	curr_skb = head_skb;
+	num = num_buf;
+
+	while (--num_buf) {
+		int num_skb_frags;
+
+		buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
+		if (unlikely(!buf)) {
+			pr_debug("%s: rx error: %d buffers out of %d missing\n",
+				 dev->name, num_buf, num);
+			dev->stats.rx_length_errors++;
+			goto err_buf;
+		}
+
+		stats->bytes += len;
+		page = virt_to_head_page(buf);
+
+		truesize = mergeable_ctx_to_truesize(ctx);
+		if (unlikely(len > truesize)) {
+			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
+				 dev->name, len, (unsigned long)ctx);
+			dev->stats.rx_length_errors++;
+			goto err_skb;
+		}
+
+		num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
+		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
+			struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
+
+			if (unlikely(!nskb))
+				goto err_skb;
+			if (curr_skb == head_skb)
+				skb_shinfo(curr_skb)->frag_list = nskb;
+			else
+				curr_skb->next = nskb;
+			curr_skb = nskb;
+			head_skb->truesize += nskb->truesize;
+			num_skb_frags = 0;
+		}
+		if (curr_skb != head_skb) {
+			head_skb->data_len += len;
+			head_skb->len += len;
+			head_skb->truesize += truesize;
+		}
+		offset = buf - page_address(page);
+		if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
+			put_page(page);
+			skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
+					     len, truesize);
+		} else {
+			skb_add_rx_frag(curr_skb, num_skb_frags, page,
+					offset, len, truesize);
+		}
+	}
+
+	return head_skb;
+
+err_skb:
+	put_page(page);
+	merge_drop_follow_bufs(dev, rq, num_buf, stats);
+err_buf:
+	stats->drops++;
+	dev_kfree_skb(head_skb);
+	return NULL;
+}
+
  static struct sk_buff *receive_small(struct net_device *dev,
  				     struct virtnet_info *vi,
  				     struct receive_queue *rq,

@@ -909,7 +1012,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  	u16 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 sk_buff *head_skb;
  	struct bpf_prog *xdp_prog;
  	unsigned int truesize = mergeable_ctx_to_truesize(ctx);
  	unsigned int headroom = mergeable_ctx_to_headroom(ctx);

@@ -1054,65 +1157,15 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,

  	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
  			       metasize, !!headroom);
-	curr_skb = head_skb;
-
-	if (unlikely(!curr_skb))
+	if (unlikely(!head_skb))
  		goto err_skb;
-	while (--num_buf) {
-		int num_skb_frags;

-		buf = virtqueue_get_buf_ctx(rq->vq, &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.rx_length_errors++;
-			goto err_buf;
-		}
-
-		stats->bytes += len;
-		page = virt_to_head_page(buf);
-
-		truesize = mergeable_ctx_to_truesize(ctx);
-		if (unlikely(len > truesize)) {
-			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
-				 dev->name, len, (unsigned long)ctx);
-			dev->stats.rx_length_errors++;
-			goto err_skb;
-		}
-
-		num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
-		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
-			struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
-
-			if (unlikely(!nskb))
-				goto err_skb;
-			if (curr_skb == head_skb)
-				skb_shinfo(curr_skb)->frag_list = nskb;
-			else
-				curr_skb->next = nskb;
-			curr_skb = nskb;
-			head_skb->truesize += nskb->truesize;
-			num_skb_frags = 0;
-		}
-		if (curr_skb != head_skb) {
-			head_skb->data_len += len;
-			head_skb->len += len;
-			head_skb->truesize += truesize;
-		}
-		offset = buf - page_address(page);
-		if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
-			put_page(page);
-			skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
-					     len, truesize);
-		} else {
-			skb_add_rx_frag(curr_skb, num_skb_frags, page,
-					offset, len, truesize);
-		}
-	}
+	if (num_buf > 1)
+		head_skb = merge_receive_follow_bufs(dev, vi, rq, head_skb,
+						     num_buf, stats);
+	if (head_skb)
+		ewma_pkt_len_add(&rq->mrg_avg_pkt_len, head_skb->len);

-	ewma_pkt_len_add(&rq->mrg_avg_pkt_len, head_skb->len);
  	return head_skb;

  err_xdp:

@@ -1120,19 +1173,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  	stats->xdp_drops++;
  err_skb:
  	put_page(page);
-	while (num_buf-- > 1) {
-		buf = virtqueue_get_buf(rq->vq, &len);
-		if (unlikely(!buf)) {
-			pr_debug("%s: rx error: %d buffers missing\n",
-				 dev->name, num_buf);
-			dev->stats.rx_length_errors++;
-			break;
-		}
-		stats->bytes += len;
-		page = virt_to_head_page(buf);
-		put_page(page);
-	}
-err_buf:
+	merge_drop_follow_bufs(dev, rq, num_buf, stats);
  	stats->drops++;
  	dev_kfree_skb(head_skb);
  xdp_xmit:

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