[4/4] gro: Optimise TCP packet reception

Submitted by Herbert Xu on Feb. 9, 2009, 4 a.m.

Details

Message ID E1LWNK4-0000o0-5h@gondolin.me.apana.org.au
State Accepted
Delegated to: David Miller
Headers show

Commit Message

Herbert Xu Feb. 9, 2009, 4 a.m.
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: Herbert Xu <herbert@gondor.apana.org.au>
---

 net/ipv4/tcp.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

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diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 73266b7..90b2f3c 100644
--- a/net/ipv4/tcp.c
+++ b/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 @@  found:
 	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;