netdev - [PATCH][net-next] net: slightly optimize eth_type

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Date:   Tue, 13 Nov 2018 09:34:31 +0800
From:   Li RongQing <lirongqing@...du.com>
To:     netdev@...r.kernel.org
Subject: [PATCH][net-next] net: slightly optimize eth_type_trans

netperf udp stream shows that eth_type_trans takes certain cpu,
so adjust the mac address check order, and firstly check if it
is device address, and only check if it is multicast address
only if not the device address.

After this change:
To unicast, and skb dst mac is device mac, this is most of time
reduce a comparision
To unicast, and skb dst mac is not device mac, nothing change
To multicast, increase a comparision

Before:
1.03%  [kernel]          [k] eth_type_trans

After:
0.78%  [kernel]          [k] eth_type_trans

Signed-off-by: Zhang Yu <zhangyu31@...du.com>
Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 net/ethernet/eth.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index fd8faa0dfa61..1c88f5c5d5b1 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -165,15 +165,17 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	eth = (struct ethhdr *)skb->data;
 	skb_pull_inline(skb, ETH_HLEN);
 
-	if (unlikely(is_multicast_ether_addr_64bits(eth->h_dest))) {
-		if (ether_addr_equal_64bits(eth->h_dest, dev->broadcast))
-			skb->pkt_type = PACKET_BROADCAST;
-		else
-			skb->pkt_type = PACKET_MULTICAST;
+	if (unlikely(!ether_addr_equal_64bits(eth->h_dest,
+						   dev->dev_addr))) {
+		if (unlikely(is_multicast_ether_addr_64bits(eth->h_dest))) {
+			if (ether_addr_equal_64bits(eth->h_dest, dev->broadcast))
+				skb->pkt_type = PACKET_BROADCAST;
+			else
+				skb->pkt_type = PACKET_MULTICAST;
+		} else {
+			skb->pkt_type = PACKET_OTHERHOST;
+		}
 	}
-	else if (unlikely(!ether_addr_equal_64bits(eth->h_dest,
-						   dev->dev_addr)))
-		skb->pkt_type = PACKET_OTHERHOST;
 
 	/*
 	 * Some variants of DSA tagging don't have an ethertype field
-- 
2.16.2