diff options
Diffstat (limited to 'net/ipv4/tcp_metrics.c')
| -rw-r--r-- | net/ipv4/tcp_metrics.c | 44 |
1 files changed, 19 insertions, 25 deletions
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c index f6a005c485a9..52f3c6b971d2 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; @@ -478,15 +478,19 @@ 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. + crtt = tcp_metric_get_jiffies(tm, TCP_METRIC_RTT); + rcu_read_unlock(); +reset: + /* The initial RTT measurement from the SYN/SYN-ACK is not ideal + * to seed the RTO for later data packets because SYN packets are + * small. Use the per-dst cached values to seed the RTO but keep + * the RTT estimator variables intact (e.g., srtt, mdev, rttvar). + * Later the RTO will be updated immediately upon obtaining the first + * data RTT sample (tcp_rtt_estimator()). Hence the cached RTT only + * influences the first RTO but not later RTT estimation. + * + * But if RTT is not available from the SYN (due to retransmits or + * syn cookies) or the cache, force a conservative 3secs timeout. * * A bit of theory. RTT is time passed after "normal" sized packet * is sent until it is ACKed. In normal circumstances sending small @@ -497,21 +501,11 @@ void tcp_init_metrics(struct sock *sk) * 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)); - } - rcu_read_unlock(); - - tcp_set_rto(sk); -reset: - if (tp->srtt == 0) { + if (crtt > tp->srtt) { + /* Set RTO like tcp_rtt_estimator(), but from cached RTT. */ + crtt >>= 3; + inet_csk(sk)->icsk_rto = crtt + max(2 * crtt, 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 |