Author: andre
Date: Sun Oct 28 17:25:08 2012
New Revision: 242250
URL: http://svn.freebsd.org/changeset/base/242250
Log:
When SYN or SYN/ACK had to be retransmitted RFC5681 requires us to
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
Modified:
head/sys/netinet/tcp_input.c
head/sys/netinet/tcp_syncache.c
head/sys/netinet/tcp_timer.c
Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c Sun Oct 28 17:16:09 2012
(r242249)
+++ head/sys/netinet/tcp_input.c Sun Oct 28 17:25:08 2012
(r242250)
@@ -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.
- */
- if (V_tcp_do_rfc3390)
+ * 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 (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 {
Modified: head/sys/netinet/tcp_syncache.c
==============================================================================
--- head/sys/netinet/tcp_syncache.c Sun Oct 28 17:16:09 2012
(r242249)
+++ head/sys/netinet/tcp_syncache.c Sun Oct 28 17:25:08 2012
(r242250)
@@ -852,11 +852,12 @@ syncache_socket(struct syncache *sc, str
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
/*
Modified: head/sys/netinet/tcp_timer.c
==============================================================================
--- head/sys/netinet/tcp_timer.c Sun Oct 28 17:16:09 2012
(r242249)
+++ head/sys/netinet/tcp_timer.c Sun Oct 28 17:25:08 2012
(r242250)
@@ -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.
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