Author: andre
Date: Wed Aug 18 18:05:54 2010
New Revision: 211464
URL: http://svn.freebsd.org/changeset/base/211464
Log:
If a TCP connection has been idle for one retransmit timeout or more
it must reset its congestion window back to the initial window.
RFC3390 has increased the initial window from 1 segment to up to
4 segments.
The initial window increase of RFC3390 wasn't reflected into the
restart window which remained at its original defaults of 4 segments
for local and 1 segment for all other connections. Both values are
controllable through sysctl net.inet.tcp.local_slowstart_flightsize
and net.inet.tcp.slowstart_flightsize.
The increase helps TCP's slow start algorithm to open up the congestion
window much faster.
Reviewed by: lstewart
MFC after: 1 week
Modified:
head/sys/netinet/tcp_output.c
head/sys/netinet/tcp_var.h
Modified: head/sys/netinet/tcp_output.c
==============================================================================
--- head/sys/netinet/tcp_output.c Wed Aug 18 17:40:10 2010
(r211463)
+++ head/sys/netinet/tcp_output.c Wed Aug 18 18:05:54 2010
(r211464)
@@ -140,7 +140,7 @@ tcp_output(struct tcpcb *tp)
{
struct socket *so = tp->t_inpcb->inp_socket;
long len, recwin, sendwin;
- int off, flags, error;
+ int off, flags, error, rw;
struct mbuf *m;
struct ip *ip = NULL;
struct ipovly *ipov = NULL;
@@ -176,23 +176,34 @@ tcp_output(struct tcpcb *tp)
idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur) {
/*
- * We have been idle for "a while" and no acks are
- * expected to clock out any data we send --
- * slow start to get ack "clock" running again.
+ * If we've been idle for more than one retransmit
+ * timeout the old congestion window is no longer
+ * current and we have to reduce it to the restart
+ * window before we can transmit again.
*
- * Set the slow-start flight size depending on whether
- * this is a local network or not.
+ * The restart window is the initial window or the last
+ * CWND, whichever is smaller.
+ *
+ * This is done to prevent us from flooding the path with
+ * a full CWND at wirespeed, overloading router and switch
+ * buffers along the way.
+ *
+ * See RFC5681 Section 4.1. "Restarting Idle Connections".
*/
- int ss = V_ss_fltsz;
+ if (V_tcp_do_rfc3390)
+ rw = min(4 * tp->t_maxseg,
+ max(2 * tp->t_maxseg, 4380));
#ifdef INET6
- if (isipv6) {
- if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
- ss = V_ss_fltsz_local;
- } else
-#endif /* INET6 */
- if (in_localaddr(tp->t_inpcb->inp_faddr))
- ss = V_ss_fltsz_local;
- tp->snd_cwnd = tp->t_maxseg * ss;
+ else if ((isipv6 ? in6_localaddr(&tp->t_inpcb->in6p_faddr) :
+ in_localaddr(tp->t_inpcb->inp_faddr)))
+#else
+ else if (in_localaddr(tp->t_inpcb->inp_faddr))
+#endif
+ rw = V_ss_fltsz_local * tp->t_maxseg;
+ else
+ rw = V_ss_fltsz * tp->t_maxseg;
+
+ tp->snd_cwnd = min(rw, tp->snd_cwnd);
}
tp->t_flags &= ~TF_LASTIDLE;
if (idle) {
Modified: head/sys/netinet/tcp_var.h
==============================================================================
--- head/sys/netinet/tcp_var.h Wed Aug 18 17:40:10 2010 (r211463)
+++ head/sys/netinet/tcp_var.h Wed Aug 18 18:05:54 2010 (r211464)
@@ -565,6 +565,7 @@ extern int tcp_log_in_vain;
VNET_DECLARE(int, tcp_mssdflt); /* XXX */
VNET_DECLARE(int, tcp_minmss);
VNET_DECLARE(int, tcp_delack_enabled);
+VNET_DECLARE(int, tcp_do_rfc3390);
VNET_DECLARE(int, tcp_do_newreno);
VNET_DECLARE(int, path_mtu_discovery);
VNET_DECLARE(int, ss_fltsz);
@@ -575,6 +576,7 @@ VNET_DECLARE(int, ss_fltsz_local);
#define V_tcp_mssdflt VNET(tcp_mssdflt)
#define V_tcp_minmss VNET(tcp_minmss)
#define V_tcp_delack_enabled VNET(tcp_delack_enabled)
+#define V_tcp_do_rfc3390 VNET(tcp_do_rfc3390)
#define V_tcp_do_newreno VNET(tcp_do_newreno)
#define V_path_mtu_discovery VNET(path_mtu_discovery)
#define V_ss_fltsz VNET(ss_fltsz)
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