diff options
| -rw-r--r-- | net/ipv4/tcp_metrics.c | 44 |
1 files changed, 11 insertions, 33 deletions
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c index f6a005c485a9..273ed735cca2 100644 --- a/net/ipv4/tcp_metrics.c +++ b/net/ipv4/tcp_metrics.c @@ -443,7 +443,7 @@ void tcp_init_metrics(struct sock *sk) struct dst_entry *dst = __sk_dst_get(sk); struct tcp_sock *tp = tcp_sk(sk); struct tcp_metrics_block *tm; - u32 val; + u32 val, crtt = 0; /* cached RTT scaled by 8 */ if (dst == NULL) goto reset; @@ -478,40 +478,18 @@ void tcp_init_metrics(struct sock *sk) tp->reordering = val; } - val = tcp_metric_get(tm, TCP_METRIC_RTT); - if (val == 0 || tp->srtt == 0) { - rcu_read_unlock(); - goto reset; - } - /* Initial rtt is determined from SYN,SYN-ACK. - * The segment is small and rtt may appear much - * less than real one. Use per-dst memory - * to make it more realistic. - * - * A bit of theory. RTT is time passed after "normal" sized packet - * is sent until it is ACKed. In normal circumstances sending small - * packets force peer to delay ACKs and calculation is correct too. - * The algorithm is adaptive and, provided we follow specs, it - * NEVER underestimate RTT. BUT! If peer tries to make some clever - * tricks sort of "quick acks" for time long enough to decrease RTT - * to low value, and then abruptly stops to do it and starts to delay - * ACKs, wait for troubles. - */ - val = msecs_to_jiffies(val); - if (val > tp->srtt) { - tp->srtt = val; - tp->rtt_seq = tp->snd_nxt; - } - val = tcp_metric_get_jiffies(tm, TCP_METRIC_RTTVAR); - if (val > tp->mdev) { - tp->mdev = val; - tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); - } + crtt = tcp_metric_get_jiffies(tm, TCP_METRIC_RTT); rcu_read_unlock(); - - tcp_set_rto(sk); reset: - if (tp->srtt == 0) { + if (crtt > tp->srtt) { + /* Initial RTT (tp->srtt) from SYN usually don't measure + * serialization delay on low BW links well so RTO may be + * under-estimated. Stay conservative and seed RTO with + * the RTTs from past data exchanges, using the same seeding + * formula in tcp_rtt_estimator(). + */ + inet_csk(sk)->icsk_rto = crtt + max(crtt >> 2, tcp_rto_min(sk)); + } else if (tp->srtt == 0) { /* RFC6298: 5.7 We've failed to get a valid RTT sample from * 3WHS. This is most likely due to retransmission, * including spurious one. Reset the RTO back to 3secs |