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>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f685324..be3686a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -274,6 +274,8 @@
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);