tcp: early retransmit: delayed fast retransmit

Implementing the advanced early retransmit (sysctl_tcp_early_retrans==2).
Delays the fast retransmit by an interval of RTT/4. We borrow the
RTO timer to implement the delay. If we receive another ACK or send
a new packet, the timer is cancelled and restored to original RTO
value offset by time elapsed.  When the delayed-ER timer fires,
we enter fast recovery and perform fast retransmit.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 3 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 834e89fc541b..d94733009923 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -78,9 +78,8 @@ static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
                 tp->frto_counter = 3;
 
         tp->packets_out += tcp_skb_pcount(skb);
-        if (!prior_packets)
-                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-                                          inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
+        if (!prior_packets || tp->early_retrans_delayed)
+                tcp_rearm_rto(sk);
 }
 
 /* SND.NXT, if window was not shrunk.