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Commit f34d1955 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by David S. Miller
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[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: default avatarStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: default avatarDavid 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