[PATCH] tun: use netif_receive_skb instead of netif_rx_ni

[Qin Chuanyu <qinchuanyu@huawei.com>]

we could xmit directly instead of going through softirq to gain 
throughput and lantency improved.
test model: VM-Host-Host just do transmit. with vhost thread and nic
interrupt bind cpu1. netperf do throuhput test and qperf do lantency test.
Host OS: suse11sp3, Guest OS: suse11sp3

latency result(us):
packet_len 64 256 512 1460
old(UDP)   44  47  48   66
new(UDP)   38  41  42   66

old(TCP)   52  55  70  117
new(TCP)   45  48  61  114

throughput result(Gbit/s):
packet_len   64   512   1024   1460
old(UDP)   0.42  2.02   3.75   4.68
new(UDP)   0.45  2.14   3.77   5.06

TCP due to the latency, client couldn't send packet big enough
to get benefit from TSO of nic, so the result show it will send
more packet per sencond but get lower throughput.

Eric mentioned that it would has problem with cgroup, but the patch
had been sent by Herbert Xu.
patch_id f845172531fb7410c7fb7780b1a6e51ee6df7d52

Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com>
---
  drivers/net/tun.c |    4 +++-
  1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 44c4db8..90b4e58 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1184,7 +1184,9 @@ static ssize_t tun_get_user(struct tun_struct 
*tun, struct tun_file *tfile,
  	skb_probe_transport_header(skb, 0);

  	rxhash = skb_get_hash(skb);
-	netif_rx_ni(skb);
+	rcu_read_lock_bh();
+	netif_receive_skb(skb);
+	rcu_read_unlock_bh();

  	tun->dev->stats.rx_packets++;
  	tun->dev->stats.rx_bytes += len;
-- 
1.7.3.1.msysgit.0