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When SYN or SYN/ACK had to be retransmitted RFC5681 requires us to

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reduce the initial CWND to one segment.  This reduction got lost
some time ago due to a change in initialization ordering.

Additionally in tcp_timer_rexmt() avoid entering fast recovery when
we're still in TCPS_SYN_SENT state.

MFC after:	2 weeks
This commit is contained in:
Andre Oppermann 2012-10-28 17:25:08 +00:00
parent 22efabd40c
commit cf8f04f4c0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=242250
3 changed files with 19 additions and 6 deletions
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12
sys/netinet/tcp_input.c
View File

@ -345,10 +345,16 @@ cc_conn_init(struct tcpcb *tp)
/*
* Set the initial slow-start flight size.
*
* RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
* XXX: We currently check only in syncache_socket for that.
* RFC5681 Section 3.1 specifies the default conservative values.
* RFC3390 specifies slightly more aggressive values.
*
* If a SYN or SYN/ACK was lost and retransmitted, we have to
* reduce the initial CWND to one segment as congestion is likely
* requiring us to be cautious.
*/
if (V_tcp_do_rfc3390)
if (tp->snd_cwnd == 1)
tp->snd_cwnd = tp->t_maxseg; /* SYN(-ACK) lost */
else if (V_tcp_do_rfc3390)
tp->snd_cwnd = min(4 * tp->t_maxseg,
max(2 * tp->t_maxseg, 4380));
else {

5
sys/netinet/tcp_syncache.c
View File

@ -852,11 +852,12 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
tcp_mss(tp, sc->sc_peer_mss);
/*
* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
* If the SYN,ACK was retransmitted, indicate that CWND to be
* limited to one segment in cc_conn_init().
* NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
*/
if (sc->sc_rxmits > 1)
tp->snd_cwnd = tp->t_maxseg;
tp->snd_cwnd = 1;
#ifdef TCP_OFFLOAD
/*

8
sys/netinet/tcp_timer.c
View File

@ -539,7 +539,13 @@ tcp_timer_rexmt(void * xtp)
}
INP_INFO_RUNLOCK(&V_tcbinfo);
headlocked = 0;
if (tp->t_rxtshift == 1) {
if (tp->t_state == TCPS_SYN_SENT) {
/*
* If the SYN was retransmitted, indicate CWND to be
* limited to 1 segment in cc_conn_init().
*/
tp->snd_cwnd = 1;
} else if (tp->t_rxtshift == 1) {
/*
* first retransmit; record ssthresh and cwnd so they can
* be recovered if this turns out to be a "bad" retransmit.