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Commit 10a8d94a authored by Jason Wang's avatar Jason Wang Committed by David S. Miller
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virtio_net: introduce VIRTIO_NET_HDR_F_DATA_VALID 



There's no need for the guest to validate the checksum if it have been
validated by host nics. So this patch introduces a new flag -
VIRTIO_NET_HDR_F_DATA_VALID which is used to bypass the checksum
examing in guest. The backend (tap/macvtap) may set this flag when
met skbs with CHECKSUM_UNNECESSARY to save cpu utilization.

No feature negotiation is needed as old driver just ignore this flag.

Iperf shows 12%-30% performance improvement for UDP traffic. For TCP,
when gro is on no difference as it produces skb with partial
checksum. But when gro is disabled, 20% or even higher improvement
could be measured by netperf.

Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 40d15cd0

drivers/net/macvtap.c

+2 −0
Original line number Diff line number Diff line
@@ -508,6 +508,8 @@ static int macvtap_skb_to_vnet_hdr(const struct sk_buff *skb, 
		vnet_hdr->flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;

		vnet_hdr->csum_start = skb_checksum_start_offset(skb);

		vnet_hdr->csum_offset = skb->csum_offset;

	} else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {

		vnet_hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;

	} /* else everything is zero */



	return 0;

drivers/net/tun.c

+2 −0
Original line number Diff line number Diff line
@@ -788,6 +788,8 @@ static ssize_t tun_put_user(struct tun_struct *tun, 
			gso.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;

			gso.csum_start = skb_checksum_start_offset(skb);

			gso.csum_offset = skb->csum_offset;

		} else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {

			gso.flags = VIRTIO_NET_HDR_F_DATA_VALID;

		} /* else everything is zero */



		if (unlikely(memcpy_toiovecend(iv, (void *)&gso, total,

drivers/net/virtio_net.c

+2 −0
Original line number Diff line number Diff line
@@ -274,6 +274,8 @@ static void receive_buf(struct net_device *dev, void *buf, unsigned int len) 
					  hdr->hdr.csum_start,

					  hdr->hdr.csum_offset))

			goto frame_err;

	} else if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID) {

		skb->ip_summed = CHECKSUM_UNNECESSARY;

	}



	skb->protocol = eth_type_trans(skb, dev);

include/linux/virtio_net.h

+1 −0
Original line number Diff line number Diff line
@@ -63,6 +63,7 @@ struct virtio_net_config { 
 * 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

#define VIRTIO_NET_HDR_F_DATA_VALID	2	// Csum is valid

	__u8 flags;

#define VIRTIO_NET_HDR_GSO_NONE		0	// Not a GSO frame

#define VIRTIO_NET_HDR_GSO_TCPV4	1	// GSO frame, IPv4 TCP (TSO)

net/packet/af_packet.c

+2 −0
Original line number Diff line number Diff line
@@ -1685,6 +1685,8 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock, 
			vnet_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;

			vnet_hdr.csum_start = skb_checksum_start_offset(skb);

			vnet_hdr.csum_offset = skb->csum_offset;

		} else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {

			vnet_hdr.flags = VIRTIO_NET_HDR_F_DATA_VALID;

		} /* else everything is zero */



		err = memcpy_toiovec(msg->msg_iov, (void *)&vnet_hdr,