tcp: tcp_transmit_skb() optimizations

1) We need to take a timestamp only for skb that should be cloned.

Other skbs are not in write queue and no rtt estimation is done on them.

2) the unlikely() hint is wrong for receivers (they send pure ACK)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: MF Nowlan <fitz@cs.yale.edu>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-By: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 2822ad021a48dbf7f9d2bc18b70b059dc51547e0..e5ce0e1d13b7f1c677336e032dd6c2b342f492ae 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -850,15 +850,15 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 
        BUG_ON(!skb || !tcp_skb_pcount(skb));
 
-       /* If congestion control is doing timestamping, we must
-        * take such a timestamp before we potentially clone/copy.
-        */
-       if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
-               __net_timestamp(skb);
-
-       if (likely(clone_it)) {
+       if (clone_it) {
                const struct sk_buff *fclone = skb + 1;
 
+               /* If congestion control is doing timestamping, we must
+                * take such a timestamp before we potentially clone/copy.
+                */
+               if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
+                       __net_timestamp(skb);
+
                if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
                             fclone->fclone == SKB_FCLONE_CLONE))
                        NET_INC_STATS_BH(sock_net(sk),