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Commit e7428e95 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
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virtio-net: put virtio net header inline with data 



For small packets we can simplify xmit processing
by linearizing buffers with the header:
most packets seem to have enough head room
we can use for this purpose.
Since existing hypervisors require that header
is the first s/g element, we need a feature bit
for this.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 10eccb46

drivers/net/virtio_net.c

+34 −8
Original line number Diff line number Diff line
@@ -106,6 +106,9 @@ struct virtnet_info { 
	/* Has control virtqueue */

	bool has_cvq;



	/* Host can handle any s/g split between our header and packet data */

	bool any_header_sg;



	/* enable config space updates */

	bool config_enable;
@@ -669,12 +672,28 @@ static void free_old_xmit_skbs(struct send_queue *sq) 


static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)

{

	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);

	struct skb_vnet_hdr *hdr;

	const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;

	struct virtnet_info *vi = sq->vq->vdev->priv;

	unsigned num_sg;

	unsigned hdr_len;

	bool can_push;



	pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);

	if (vi->mergeable_rx_bufs)

		hdr_len = sizeof hdr->mhdr;

	else

		hdr_len = sizeof hdr->hdr;



	can_push = vi->any_header_sg &&

		!((unsigned long)skb->data & (__alignof__(*hdr) - 1)) &&

		!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len;

	/* Even if we can, don't push here yet as this would skew

	 * csum_start offset below. */

	if (can_push)

		hdr = (struct skb_vnet_hdr *)(skb->data - hdr_len);

	else

		hdr = skb_vnet_hdr(skb);



	if (skb->ip_summed == CHECKSUM_PARTIAL) {

		hdr->hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
@@ -703,15 +722,18 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb) 
		hdr->hdr.gso_size = hdr->hdr.hdr_len = 0;

	}



	hdr->mhdr.num_buffers = 0;



	/* Encode metadata header at front. */

	if (vi->mergeable_rx_bufs)

		sg_set_buf(sq->sg, &hdr->mhdr, sizeof hdr->mhdr);

	else

		sg_set_buf(sq->sg, &hdr->hdr, sizeof hdr->hdr);

		hdr->mhdr.num_buffers = 0;



	if (can_push) {

		__skb_push(skb, hdr_len);

		num_sg = skb_to_sgvec(skb, sq->sg, 0, skb->len);

		/* Pull header back to avoid skew in tx bytes calculations. */

		__skb_pull(skb, hdr_len);

	} else {

		sg_set_buf(sq->sg, hdr, hdr_len);

		num_sg = skb_to_sgvec(skb, sq->sg + 1, 0, skb->len) + 1;

	}

	return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);

}
@@ -1552,6 +1574,9 @@ static int virtnet_probe(struct virtio_device *vdev) 
	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))

		vi->mergeable_rx_bufs = true;



	if (virtio_has_feature(vdev, VIRTIO_F_ANY_LAYOUT))

		vi->any_header_sg = true;



	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))

		vi->has_cvq = true;
@@ -1727,6 +1752,7 @@ static unsigned int features[] = { 
	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,

	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,

	VIRTIO_NET_F_CTRL_MAC_ADDR,

	VIRTIO_F_ANY_LAYOUT,

};



static struct virtio_driver virtio_net_driver = {

include/uapi/linux/virtio_net.h

+3 −1
Original line number Diff line number Diff line
@@ -70,7 +70,9 @@ struct virtio_net_config { 
	__u16 max_virtqueue_pairs;

} __attribute__((packed));



/* This is the first element of the scatter-gather list.  If you don't

/* This header comes first in the scatter-gather list.

 * If VIRTIO_F_ANY_LAYOUT is not negotiated, it must

 * be the first element of the scatter-gather list.  If you don't

 * specify GSO or CSUM features, you can simply ignore the header. */

struct virtio_net_hdr {

#define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	// Use csum_start, csum_offset