Date: Tue, 20 Aug 2002 14:28:05 -0700 (PDT) From: Oleg Polyakov <opolyakov@yahoo.com> To: freebsd-net@freebsd.org Subject: Re: Initial congestion window increase Message-ID: <20020820212805.58712.qmail@web10408.mail.yahoo.com>
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Attached below revamped patches to introduce RFC 2414 -
'Increasing TCP's Initial Window' to FreeBSD.
Patches add sysctl variable
- net.inet.tcp.increased_initial_window which is turned off by now.
They also change initial and restart congestion windows in
accordance with RFC. The restart window value set to minimum
between initial window and current congestion window.
The change in tcp_subr.c for cwnd decreasing in case of MTU
discovery lowering mss is about the same as in OpenBSD, which
as far as I can tell implementing only that part of RFC 2414.
Suggestions and opinions are appreciated.
----
Oleg
--- tcp_input.c.orig Wed Jul 31 19:06:49 2002
+++ tcp_input.c Thu Aug 15 13:59:19 2002
@@ -121,6 +121,10 @@
&tcp_delack_enabled, 0,
"Delay ACK to try and piggyback it onto a data packet");
+int inc_init_win = 0;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, increased_initial_window, CTLFLAG_RW,
+ &inc_init_win, 1, "Increased initial window");
+
#ifdef TCP_DROP_SYNFIN
static int drop_synfin = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
@@ -2492,6 +2496,7 @@
* of the interface), as we can't discover anything about intervening
* gateways or networks. We also initialize the congestion/slow start
* window to be a single segment if the destination isn't local.
+ * We may increase the congestion/slow start window in accordance with
RFC2414.
* While looking at the routing entry, we also initialize other path-dependent
* parameters from pre-set or cached values in the routing entry.
*
@@ -2710,7 +2715,9 @@
#endif
)
tp->snd_cwnd = mss * ss_fltsz_local;
- else
+ else if (inc_init_win)
+ tp->snd_cwnd = min(4*mss, max(2*mss,4380));
+ else
tp->snd_cwnd = mss * ss_fltsz;
if (rt->rt_rmx.rmx_ssthresh) {
--- tcp_output.c.orig Thu Aug 15 13:55:52 2002
+++ tcp_output.c Fri Aug 16 13:24:40 2002
@@ -146,16 +146,22 @@
* Set the slow-start flight size depending on whether
* this is a local network or not.
*/
- int ss = ss_fltsz;
+ if (
#ifdef INET6
- if (isipv6) {
- if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
- ss = ss_fltsz_local;
- } else
+ (isipv6 && in6_localaddr(&tp->t_inpcb->in6p_faddr)) ||
+ (!isipv6 &&
#endif /* INET6 */
- if (in_localaddr(tp->t_inpcb->inp_faddr))
- ss = ss_fltsz_local;
- tp->snd_cwnd = tp->t_maxseg * ss;
+ in_localaddr(tp->t_inpcb->inp_faddr)
+#ifdef INET6
+ )
+#endif /* INET6 */
+ )
+ tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
+ else if (inc_init_win)
+ tp->snd_cwnd = min(tp->snd_cwnd,min(4*tp->t_maxseg,
+ max(2*tp->t_maxseg,4380)));
+ else
+ tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
}
tp->t_flags &= ~TF_LASTIDLE;
if (idle) {
--- tcp_subr.c.orig Thu Aug 1 03:54:43 2002
+++ tcp_subr.c Fri Aug 16 14:52:16 2002
@@ -1385,6 +1385,14 @@
#endif
if (so->so_snd.sb_hiwat < mss)
mss = so->so_snd.sb_hiwat;
+ /*
+ * Follow suggestion in RFC 2414 to reduce the congestion
+ * window by the ratio of the old segment size to the new
+ * segment size.
+ */
+ if (mss < tp->t_maxseg)
+ tp->snd_cwnd = max((tp->snd_cwnd / tp->t_maxseg) *
+ mss, mss);
tp->t_maxseg = mss;
--- tcp_var.h.orig Mon Aug 12 15:53:19 2002
+++ tcp_var.h Fri Aug 16 15:44:57 2002
@@ -436,6 +436,7 @@
extern int path_mtu_discovery;
extern int ss_fltsz;
extern int ss_fltsz_local;
+extern int inc_init_win;
void tcp_canceltimers(struct tcpcb *);
struct tcpcb *
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