Hi,
RFC 5681 Section 3.1 has an Implementation Note that covers the bug fixed by
the following patch. I ran into this bug testing on a high latency link. My
congestion window was pinned to a specific value and could not open further,
causing a lack of bandwidth utilization.
I chose if/assign rather than max(9) for clarity with the RFC; however, both
work fine.
Cheers,
Brian
Index: tcp_input.c
===================================================================
RCS file: /home/brian/cvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.364
diff -u -r1.364 tcp_input.c
--- tcp_input.c 6 Dec 2019 14:43:14 -0000 1.364
+++ tcp_input.c 1 Jun 2020 21:16:26 -0000
@@ -1707,8 +1707,11 @@
u_int cw = tp->snd_cwnd;
u_int incr = tp->t_maxseg;
- if (cw > tp->snd_ssthresh)
+ if (cw > tp->snd_ssthresh) {
incr = incr * incr / cw;
+ if (incr == 0)
+ incr = 1;
+ }
if (tp->t_dupacks < tcprexmtthresh)
tp->snd_cwnd = ulmin(cw + incr,
TCP_MAXWIN << tp->snd_scale);
