From 6e26dd0dbea6e240e25b9e63f31e0563317bb925 Mon Sep 17 00:00:00 2001 From: Richard Scheffenegger Date: Wed, 24 Jun 2020 13:52:53 +0000 Subject: [PATCH] TCP: fix cubic RTO reaction. Proper TCP Cubic operation requires the knowledge of the maximum congestion window prior to the last congestion event. This restores and improves a bugfix previously added by jtl@ but subsequently removed due to a revert. Reported by: chengc_netapp.com Reviewed by: chengc_netapp.com, tuexen (mentor) Approved by: tuexen (mentor), rgrimes (mentor) MFC after: 2 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D25133 --- sys/netinet/cc/cc_cubic.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c index cec5917e01b3..a98c1c5c75be 100644 --- a/sys/netinet/cc/cc_cubic.c +++ b/sys/netinet/cc/cc_cubic.c @@ -313,10 +313,15 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type) * timeout has fired more than once, as there is a reasonable * chance the first one is a false alarm and may not indicate * congestion. + * This will put Cubic firmly into the concave / TCP friendly + * region, for a slower ramp-up after two consecutive RTOs. */ if (CCV(ccv, t_rxtshift) >= 2) { cubic_data->flags |= CUBICFLAG_CONG_EVENT; cubic_data->t_last_cong = ticks; + cubic_data->max_cwnd = CCV(ccv, snd_cwnd_prev); + cubic_data->K = cubic_k(cubic_data->max_cwnd / + CCV(ccv, t_maxseg)); } break; }