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authorJason Wang <jasowang@redhat.com>2011-06-10 00:56:17 +0000
committerDavid S. Miller <davem@davemloft.net>2011-06-11 15:57:47 -0700
commit10a8d94a95742bb15b4e617ee9884bb4381362be (patch)
tree768f2d92be0e12bca791bcb901ad4bdedc7d8a76 /drivers/net/tun.c
parent40d15cd06e87722b1cc27d56c8274617580f2c56 (diff)
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>
Diffstat (limited to 'drivers/net/tun.c')
-rw-r--r--drivers/net/tun.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index ef68e13c042d..4dab85eecb60 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -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,