Commit f34d1955 authored Aug 07, 2007 by Stephen Hemminger Committed by David S. Miller Aug 07, 2007

[TCP]: H-TCP maxRTT estimation at startup



Small patch to H-TCP from Douglas Leith. 

Fix estimation of maxRTT.  The original code ignores rtt measurements
during slow start (via the check tp->snd_ssthresh < 0xFFFF) yet this
is probably a good time to try to estimate max rtt as delayed acking
is disabled and slow start will only exit on a loss which presumably
corresponds to a maxrtt measurement.  Second, the original code (via
the check htcp_ccount(ca) > 3) ignores rtt data during what it
estimates to be the first 3 round-trip times.  This seems like an
unnecessary check now that the RCV timestamp are no longer used
for rtt estimation.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 591e6206

net/ipv4/tcp_htcp.c

+1 −3

Original line number	Diff line number	Diff line
		@@ -79,7 +79,6 @@ static u32 htcp_cwnd_undo(struct sock *sk)
		static inline void measure_rtt(struct sock *sk, u32 srtt)
		{
		const struct inet_connection_sock *icsk = inet_csk(sk);
		const struct tcp_sock *tp = tcp_sk(sk);
		struct htcp *ca = inet_csk_ca(sk);

		/* keep track of minimum RTT seen so far, minRTT is zero at first */
		@@ -87,8 +86,7 @@ static inline void measure_rtt(struct sock *sk, u32 srtt)
		ca->minRTT = srtt;

		/* max RTT */
		if (icsk->icsk_ca_state == TCP_CA_Open
		&& tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
		if (icsk->icsk_ca_state == TCP_CA_Open) {
		if (ca->maxRTT < ca->minRTT)
		ca->maxRTT = ca->minRTT;
		if (ca->maxRTT < srtt

Admin message