tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open side
This patch lowers the default initRTO from 3secs to 1sec per
RFC2988bis. It falls back to 3secs if the SYN or SYN-ACK packet
has been retransmitted, AND the TCP timestamp option is not on.
It also adds support to take RTT sample during 3WHS on the passive
open side, just like its active open counterpart, and uses it, if
valid, to seed the initRTO for the data transmission phase.
The patch also resets ssthresh to its initial default at the
beginning of the data transmission phase, and reduces cwnd to 1 if
there has been MORE THAN ONE retransmission during 3WHS per RFC5681.
Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a7d6671..617dee3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -429,8 +429,8 @@
break;
icsk->icsk_backoff--;
- inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) <<
- icsk->icsk_backoff;
+ inet_csk(sk)->icsk_rto = (tp->srtt ? __tcp_set_rto(tp) :
+ TCP_TIMEOUT_INIT) << icsk->icsk_backoff;
tcp_bound_rto(sk);
skb = tcp_write_queue_head(sk);
@@ -1384,6 +1384,7 @@
isn = tcp_v4_init_sequence(skb);
}
tcp_rsk(req)->snt_isn = isn;
+ tcp_rsk(req)->snt_synack = tcp_time_stamp;
if (tcp_v4_send_synack(sk, dst, req,
(struct request_values *)&tmp_ext) ||
@@ -1458,6 +1459,10 @@
newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;
tcp_initialize_rcv_mss(newsk);
+ if (tcp_rsk(req)->snt_synack)
+ tcp_valid_rtt_meas(newsk,
+ tcp_time_stamp - tcp_rsk(req)->snt_synack);
+ newtp->total_retrans = req->retrans;
#ifdef CONFIG_TCP_MD5SIG
/* Copy over the MD5 key from the original socket */
@@ -1854,7 +1859,7 @@
* algorithms that we must have the following bandaid to talk
* efficiently to them. -DaveM
*/
- tp->snd_cwnd = 2;
+ tp->snd_cwnd = TCP_INIT_CWND;
/* See draft-stevens-tcpca-spec-01 for discussion of the
* initialization of these values.