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>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 136040bba3e3..970d5a2a9047 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -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)