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tcp: fix SYNACK RTT estimation in Fast Open

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tp->lsndtime may not always be the SYNACK timestamp if a passive
Fast Open socket sends data before handshake completes. And if the
remote acknowledges both the data and the SYNACK, the RTT sample
is already taken in tcp_ack(), so no need to call
tcp_update_ack_rtt() in tcp_synack_rtt_meas() aagain.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2013-10-24 08:44:25 -07:00 committed by David S. Miller
parent e9e2a904ef
commit bc15afa39e
1 changed files with 13 additions and 5 deletions
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18
net/ipv4/tcp_input.c
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@ -2871,14 +2871,19 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
}
/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
static void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)
{
struct tcp_sock *tp = tcp_sk(sk);
s32 seq_rtt = -1;
if (tp->lsndtime && !tp->total_retrans)
seq_rtt = tcp_time_stamp - tp->lsndtime;
tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt, -1);
if (synack_stamp && !tp->total_retrans)
seq_rtt = tcp_time_stamp - synack_stamp;
/* If the ACK acks both the SYNACK and the (Fast Open'd) data packets
* sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()
*/
if (!tp->srtt)
tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt, -1);
}
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
@ -5587,6 +5592,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
struct request_sock *req;
int queued = 0;
bool acceptable;
u32 synack_stamp;
tp->rx_opt.saw_tstamp = 0;
@ -5669,9 +5675,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
* so release it.
*/
if (req) {
synack_stamp = tcp_rsk(req)->snt_synack;
tp->total_retrans = req->num_retrans;
reqsk_fastopen_remove(sk, req, false);
} else {
synack_stamp = tp->lsndtime;
/* Make sure socket is routed, for correct metrics. */
icsk->icsk_af_ops->rebuild_header(sk);
tcp_init_congestion_control(sk);
@ -5694,7 +5702,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
tcp_synack_rtt_meas(sk, req);
tcp_synack_rtt_meas(sk, synack_stamp);
if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;