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TCP: fix cubic RTO reaction.

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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
This commit is contained in:
Richard Scheffenegger 2020-06-24 13:52:53 +00:00
parent 9dc7d8a246
commit 6e26dd0dbe
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=362580
1 changed files with 5 additions and 0 deletions
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5
sys/netinet/cc/cc_cubic.c
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@ -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;
}