diff options
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 65cf90e063d5..227cba79fa6b 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -671,6 +671,7 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt) { struct tcp_sock *tp = tcp_sk(sk); long m = mrtt; /* RTT */ + u32 srtt = tp->srtt; /* The following amusing code comes from Jacobson's * article in SIGCOMM '88. Note that rtt and mdev @@ -688,11 +689,9 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt) * does not matter how to _calculate_ it. Seems, it was trap * that VJ failed to avoid. 8) */ - if (m == 0) - m = 1; - if (tp->srtt != 0) { - m -= (tp->srtt >> 3); /* m is now error in rtt est */ - tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */ + if (srtt != 0) { + m -= (srtt >> 3); /* m is now error in rtt est */ + srtt += m; /* rtt = 7/8 rtt + 1/8 new */ if (m < 0) { m = -m; /* m is now abs(error) */ m -= (tp->mdev >> 2); /* similar update on mdev */ @@ -723,11 +722,12 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt) } } else { /* no previous measure. */ - tp->srtt = m << 3; /* take the measured time to be rtt */ + srtt = m << 3; /* take the measured time to be rtt */ tp->mdev = m << 1; /* make sure rto = 3*rtt */ tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); tp->rtt_seq = tp->snd_nxt; } + tp->srtt = max(1U, srtt); } /* Set the sk_pacing_rate to allow proper sizing of TSO packets. @@ -746,8 +746,10 @@ static void tcp_update_pacing_rate(struct sock *sk) rate *= max(tp->snd_cwnd, tp->packets_out); - /* Correction for small srtt : minimum srtt being 8 (1 jiffy << 3), - * be conservative and assume srtt = 1 (125 us instead of 1.25 ms) + /* Correction for small srtt and scheduling constraints. + * For small rtt, consider noise is too high, and use + * the minimal value (srtt = 1 -> 125 us for HZ=1000) + * * We probably need usec resolution in the future. * Note: This also takes care of possible srtt=0 case, * when tcp_rtt_estimator() was not yet called. |