Commit fb32856b authored by Xuan Zhuo's avatar Xuan Zhuo Committed by David S. Miller
Browse files

virtio-net: page_to_skb() use build_skb when there's sufficient tailroom 



In page_to_skb(), if we have enough tailroom to save skb_shared_info, we
can use build_skb to create skb directly. No need to alloc for
additional space. And it can save a 'frags slot', which is very friendly
to GRO.

Here, if the payload of the received package is too small (less than
GOOD_COPY_LEN), we still choose to copy it directly to the space got by
napi_alloc_skb. So we can reuse these pages.

Testing Machine:
    The four queues of the network card are bound to the cpu1.

Test command:
    for ((i=0;i<5;++i)); do sockperf tp --ip 192.168.122.64 -m 1000 -t 150& done

The size of the udp package is 1000, so in the case of this patch, there
will always be enough tailroom to use build_skb. The sent udp packet
will be discarded because there is no port to receive it. The irqsoftd
of the machine is 100%, we observe the received quantity displayed by
sar -n DEV 1:

no build_skb:  956864.00 rxpck/s
build_skb:    1158465.00 rxpck/s

Signed-off-by: default avatarXuan Zhuo <xuanzhuo@linux.alibaba.com>
Suggested-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fa588eba

drivers/net/virtio_net.c

+48 −21
Original line number Diff line number Diff line
@@ -379,21 +379,17 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, 
				   struct receive_queue *rq,

				   struct page *page, unsigned int offset,

				   unsigned int len, unsigned int truesize,

				   bool hdr_valid, unsigned int metasize)

				   bool hdr_valid, unsigned int metasize,

				   unsigned int headroom)

{

	struct sk_buff *skb;

	struct virtio_net_hdr_mrg_rxbuf *hdr;

	unsigned int copy, hdr_len, hdr_padded_len;

	char *p;

	int tailroom, shinfo_size;

	char *p, *hdr_p;



	p = page_address(page) + offset;



	/* copy small packet so we can reuse these pages for small data */

	skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);

	if (unlikely(!skb))

		return NULL;



	hdr = skb_vnet_hdr(skb);

	hdr_p = p;



	hdr_len = vi->hdr_len;

	if (vi->mergeable_rx_bufs)
@@ -401,14 +397,38 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, 
	else

		hdr_padded_len = sizeof(struct padded_vnet_hdr);



	/* hdr_valid means no XDP, so we can copy the vnet header */

	if (hdr_valid)

		memcpy(hdr, p, hdr_len);

	/* If headroom is not 0, there is an offset between the beginning of the

	 * data and the allocated space, otherwise the data and the allocated

	 * space are aligned.

	 */

	if (headroom) {

		/* The actual allocated space size is PAGE_SIZE. */

		truesize = PAGE_SIZE;

		tailroom = truesize - len - offset;

	} else {

		tailroom = truesize - len;

	}



	len -= hdr_len;

	offset += hdr_padded_len;

	p += hdr_padded_len;



	shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));



	if (len > GOOD_COPY_LEN && tailroom >= shinfo_size) {

		skb = build_skb(p, truesize);

		if (unlikely(!skb))

			return NULL;



		skb_put(skb, len);

		goto ok;

	}



	/* copy small packet so we can reuse these pages for small data */

	skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);

	if (unlikely(!skb))

		return NULL;



	/* Copy all frame if it fits skb->head, otherwise

	 * we let virtio_net_hdr_to_skb() and GRO pull headers as needed.

	 */
@@ -418,11 +438,6 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, 
		copy = ETH_HLEN + metasize;

	skb_put_data(skb, p, copy);



	if (metasize) {

		__skb_pull(skb, metasize);

		skb_metadata_set(skb, metasize);

	}



	len -= copy;

	offset += copy;
@@ -431,7 +446,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, 
			skb_add_rx_frag(skb, 0, page, offset, len, truesize);

		else

			put_page(page);

		return skb;

		goto ok;

	}



	/*
@@ -458,6 +473,18 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, 
	if (page)

		give_pages(rq, page);



ok:

	/* hdr_valid means no XDP, so we can copy the vnet header */

	if (hdr_valid) {

		hdr = skb_vnet_hdr(skb);

		memcpy(hdr, hdr_p, hdr_len);

	}



	if (metasize) {

		__skb_pull(skb, metasize);

		skb_metadata_set(skb, metasize);

	}



	return skb;

}
@@ -808,7 +835,7 @@ static struct sk_buff *receive_big(struct net_device *dev, 
{

	struct page *page = buf;

	struct sk_buff *skb =

		page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0);

		page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0, 0);



	stats->bytes += len - vi->hdr_len;

	if (unlikely(!skb))
@@ -922,7 +949,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, 
				put_page(page);

				head_skb = page_to_skb(vi, rq, xdp_page, offset,

						       len, PAGE_SIZE, false,

						       metasize);

						       metasize, headroom);

				return head_skb;

			}

			break;
@@ -980,7 +1007,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, 
	}



	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,

			       metasize);

			       metasize, headroom);

	curr_skb = head_skb;



	if (unlikely(!curr_skb))