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Work around an integer division resulting in 0 and thus the

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congestion window not being incremented, if cwnd > maxseg^2.
As suggested in RFC2581 increment the cwnd by 1 in this case.

See http://caia.swin.edu.au/reports/080829A/CAIA-TR-080829A.pdf
for more details.

Submitted by:	Alana Huebner, Lawrence Stewart,
		Grenville Armitage (caia.swin.edu.au)
Reviewed by:	dwmalone, gnn, rpaulo
MFC After:	3 days
This commit is contained in:
bz 2008-09-09 07:35:21 +00:00
parent ee52a364f7
commit c60eddf2cd
1 changed files with 3 additions and 1 deletions
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4
sys/netinet/tcp_input.c
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@ -2086,13 +2086,15 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
* in flight, open exponentially (maxseg per packet).
* Otherwise open linearly: maxseg per window
* (maxseg^2 / cwnd per packet).
* If cwnd > maxseg^2, fix the cwnd increment at 1 byte
* to avoid capping cwnd (as suggested in RFC2581).
*/
if ((!V_tcp_do_newreno && !(tp->t_flags & TF_SACK_PERMIT)) ||
!IN_FASTRECOVERY(tp)) {
u_int cw = tp->snd_cwnd;
u_int incr = tp->t_maxseg;
if (cw > tp->snd_ssthresh)
incr = incr * incr / cw;
incr = max((incr * incr / cw), 1);
tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
}
SOCKBUF_LOCK(&so->so_snd);