netdev - RE: ipgre rss is broken since gro

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Date:	Mon, 10 Dec 2012 08:54:31 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dmitry Kravkov <dmitry@...adcom.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: ipgre rss is broken since gro

On Mon, 2012-12-10 at 11:32 +0000, Dmitry Kravkov wrote:

> CPU is not loaded at all 
> 
> > cat /proc/net/softnet_stat
> Please find attached.
> 
> For gre interface RX and DROP statistics are advancing simultaneously (by one each ICMP request):
> 
> [root@ ~]# ifconfig gre
> gre       Link encap:UNSPEC  HWaddr C0-A8-0A-40-73-72-83-D2-00-00-00-00-00-00-00-00
>           inet addr:8.0.0.1  P-t-P:8.0.0.1  Mask:255.255.255.0
>           inet6 addr: fe80::5efe:c0a8:a40/64 Scope:Link
>           UP POINTOPOINT RUNNING NOARP  MTU:1476  Metric:1
>           RX packets:1646824 errors:0 dropped:51610 overruns:0 frame:0
>           TX packets:140519 errors:1 dropped:0 overruns:0 carrier:1
>           collisions:0 txqueuelen:0
>           RX bytes:2357650904 (2.1 GiB)  TX bytes:7309072 (6.9 MiB)


dropped:51610  so obviously  one cpu is fully loaded.

I believe performance problem might come from the
skb_set_queue_mapping(skb, 0); in __skb_tunnel_rx()

So all packets are queued into a single GRO queue, instead of being
split as intended in multiple queues.

I cant find why we must clear queue_mapping, so could you try :


diff --git a/include/net/dst.h b/include/net/dst.h
index 9a78810..4cb27df 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -329,7 +329,6 @@ static inline void __skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev)
 	 */
 	if (!skb->l4_rxhash)
 		skb->rxhash = 0;
-	skb_set_queue_mapping(skb, 0);
 	skb_dst_drop(skb);
 	nf_reset(skb);
 }



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