gro: Optimise TCP packet reception

gro: Optimise TCP packet reception

As this function can be called more than half a million times for
10GbE, it's important to optimise it as much as we can.

This patch uses bit ops to logical ops, as well as open coding
memcmp to exploit alignment properties.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2478,9 +2478,9 @@ struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	struct tcphdr *th2;
 	unsigned int thlen;
 	unsigned int flags;
-	unsigned int total;
 	unsigned int mss = 1;
 	int flush = 1;
+	int i;
 
 	th = skb_gro_header(skb, sizeof(*th));
 	if (unlikely(!th))
@@ -2504,7 +2504,7 @@ struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 
 		th2 = tcp_hdr(p);
 
-		if (th->source != th2->source || th->dest != th2->dest) {
+		if ((th->source ^ th2->source) | (th->dest ^ th2->dest)) {
 			NAPI_GRO_CB(p)->same_flow = 0;
 			continue;
 		}
@@ -2519,14 +2519,15 @@ struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	flush |= flags & TCP_FLAG_CWR;
 	flush |= (flags ^ tcp_flag_word(th2)) &
 		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH);
-	flush |= th->ack_seq != th2->ack_seq || th->window != th2->window;
-	flush |= memcmp(th + 1, th2 + 1, thlen - sizeof(*th));
+	flush |= (th->ack_seq ^ th2->ack_seq) | (th->window ^ th2->window);
+	for (i = sizeof(*th); !flush && i < thlen; i += 4)
+		flush |= *(u32 *)((u8 *)th + i) ^
+			 *(u32 *)((u8 *)th2 + i);
 
-	total = skb_gro_len(p);
 	mss = skb_shinfo(p)->gso_size;
 
-	flush |= skb_gro_len(skb) > mss || !skb_gro_len(skb);
-	flush |= ntohl(th2->seq) + total != ntohl(th->seq);
+	flush |= (skb_gro_len(skb) > mss) | !skb_gro_len(skb);
+	flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);
 
 	if (flush || skb_gro_receive(head, skb)) {
 		mss = 1;