netdev - [PATCH v2 net-next 6/8] tcp: tcp_mtu_probe() is likely to exit early

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Date:   Sat,  3 Dec 2016 11:14:55 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH v2 net-next 6/8] 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@...gle.com>
---
 net/ipv4/tcp_output.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index d5c46749adab..5f04bee4c86a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1932,26 +1932,26 @@ static inline void tcp_mtu_check_reprobe(struct sock *sk)
  */
 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,
-- 
2.8.0.rc3.226.g39d4020