1 files changed, 10 insertions, 8 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 65cf90e..227cba7 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.