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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: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Wang 2011-06-10 00:56:17 +00:00 committed by David S. Miller
parent 40d15cd06e
commit 10a8d94a95
5 changed files with 9 additions and 0 deletions
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2
drivers/net/macvtap.c
View File

@ -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;

2
drivers/net/tun.c
View File

@ -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,

2
drivers/net/virtio_net.c
View File

@ -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);

1
include/linux/virtio_net.h
View File

@ -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)

2
net/packet/af_packet.c
View File

@ -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,