openwrtv3/target/linux/generic/backport-4.9/024-6-tcp-tcp_mtu_probe-is-likely-to-exit-early.patch

From 12a59abc22d6664f7d3944f625ceefee92de8820 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Sat, 3 Dec 2016 11:14:55 -0800
Subject: [PATCH 06/10] tcp: tcp_mtu_probe() is likely to exit early

Adding a likely() in tcp_mtu_probe() moves its code which used to
be inlined in front of tcp_write_xmit()

We still have a cache line miss to access icsk->icsk_mtup.enabled,
we will probably have to reorganize fields to help data locality.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/ipv4/tcp_output.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1948,26 +1948,26 @@ static bool tcp_can_coalesce_send_queue_
  */
 static int tcp_mtu_probe(struct sock *sk)
 {
-	struct tcp_sock *tp = tcp_sk(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb, *nskb, *next;
 	struct net *net = sock_net(sk);
-	int len;
 	int probe_size;
 	int size_needed;
-	int copy;
+	int copy, len;
 	int mss_now;
 	int interval;
 
 	/* Not currently probing/verifying,
 	 * not in recovery,
 	 * have enough cwnd, and
-	 * not SACKing (the variable headers throw things off) */
-	if (!icsk->icsk_mtup.enabled ||
-	    icsk->icsk_mtup.probe_size ||
-	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
-	    tp->snd_cwnd < 11 ||
-	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
+	 * not SACKing (the variable headers throw things off)
+	 */
+	if (likely(!icsk->icsk_mtup.enabled ||
+		   icsk->icsk_mtup.probe_size ||
+		   inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
+		   tp->snd_cwnd < 11 ||
+		   tp->rx_opt.num_sacks || tp->rx_opt.dsack))
 		return -1;
 
 	/* Use binary search for probe_size between tcp_mss_base,