svn commit: r362580 - head/sys/netinet/cc
Richard Scheffenegger
rscheff at FreeBSD.org
Wed Jun 24 13:52:54 UTC 2020
Author: rscheff
Date: Wed Jun 24 13:52:53 2020
New Revision: 362580
URL: https://svnweb.freebsd.org/changeset/base/362580
Log:
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
Modified:
head/sys/netinet/cc/cc_cubic.c
Modified: head/sys/netinet/cc/cc_cubic.c
==============================================================================
--- head/sys/netinet/cc/cc_cubic.c Wed Jun 24 13:49:30 2020 (r362579)
+++ head/sys/netinet/cc/cc_cubic.c Wed Jun 24 13:52:53 2020 (r362580)
@@ -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;
}
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