[PATCH net-next-2.6] ipip: enable lockless xmits

[Eric Dumazet <eric.dumazet@gmail.com>]

IPIP tunnels can benefit from lockless xmits, using NETIF_F_LLTX


Bench on a 16 cpus machine (dual E5540 cpus), 16 threads sending
10000000 UDP frames via one ipip tunnel (size:200 bytes per frame)

Before patch : 
real	2m53.321s
user	0m10.277s
sys	46m0.597s


After patch:
real	0m32.063s
user	0m9.237s
sys	8m16.255s


Last problem to solve is the contention on dst :

16118.00 28.3% __ip_route_output_key         vmlinux
 6135.00 10.8% dst_release                   vmlinux
 3220.00  5.6% ip_finish_output              vmlinux
 2149.00  3.8% ip_route_output_flow          vmlinux
 1575.00  2.8% ip_append_data                vmlinux
 1481.00  2.6% ip_push_pending_frames        vmlinux
 1349.00  2.4% __xfrm_lookup                 vmlinux
 1216.00  2.1% csum_partial_copy_generic     vmlinux
 1208.00  2.1% udp_sendmsg                   vmlinux


Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 net/ipv4/ipip.c |    1 +
 1 files changed, 1 insertion(+)

diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 12b6fde..6ad46c2 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -767,6 +767,7 @@ static void ipip_tunnel_setup(struct net_device *dev)
 	dev->iflink		= 0;
 	dev->addr_len		= 4;
 	dev->features		|= NETIF_F_NETNS_LOCAL;
+	dev->features		|= NETIF_F_LLTX;
 	dev->priv_flags		&= ~IFF_XMIT_DST_RELEASE;
 }