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Diffstat (limited to 'net/ipv4/tcp_metrics.c')
-rw-r--r--net/ipv4/tcp_metrics.c42
1 files changed, 17 insertions, 25 deletions
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index f6a005c485a9..4a22f3e715df 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 +501,9 @@ 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) {
+ 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