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TCP Cubic: After leaving slowstart fix unintended cwnd jump.

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Initializing K to zero in D23655 introduced a miscalculation,
where cwnd would suddenly jump to cwnd_max instead of gradually
increasing, after leaving slow-start.

Properly calculating K instead of resetting it to zero resolves
this issue. Also making sure, that cwnd is recalculated at the
earliest opportunity once slow-start is over.

Reported by:	chengc_netapp.com
Reviewed by:	chengc_netapp.com, tuexen (mentor), rgrimes (mentor)
Approved by:	tuexen (mentor), rgrimes (mentor)
MFC after:	3 weeks
Sponsored by:	NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D25746
This commit is contained in:
Richard Scheffenegger 2020-08-13 16:38:51 +00:00
parent f359d6ebbc
commit 2bb6dfabbe
1 changed files with 13 additions and 11 deletions
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24
sys/netinet/cc/cc_cubic.c
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@ -132,19 +132,29 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
/*
* Regular ACK and we're not in cong/fast recovery and we're cwnd
* limited and we're either not doing ABC or are slow starting or are
* doing ABC and we've sent a cwnd's worth of bytes.
* limited and we're either not doing ABC or are just coming out
* from slow-start or were application limited or are slow starting
* or are doing ABC and we've sent a cwnd's worth of bytes.
*/
if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
(ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
(cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | CUBICFLAG_IN_APPLIMIT)) ||
CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
(V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
(V_tcp_do_rfc3465 && (ccv->flags & CCF_ABC_SENTAWND)))) {
/* Use the logic in NewReno ack_received() for slow start. */
if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
cubic_data->min_rtt_ticks == TCPTV_SRTTBASE) {
cubic_data->flags |= CUBICFLAG_IN_SLOWSTART;
newreno_cc_algo.ack_received(ccv, type);
} else {
if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART |
CUBICFLAG_IN_APPLIMIT)) {
cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART |
CUBICFLAG_IN_APPLIMIT);
cubic_data->t_last_cong = ticks;
cubic_data->K = cubic_k(cubic_data->max_cwnd /
CCV(ccv, t_maxseg));
}
if ((ticks_since_cong =
ticks - cubic_data->t_last_cong) < 0) {
/*
@ -153,14 +163,6 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
ticks_since_cong = INT_MAX;
cubic_data->t_last_cong = ticks - INT_MAX;
}
if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART |
CUBICFLAG_IN_APPLIMIT)) {
cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART |
CUBICFLAG_IN_APPLIMIT);
cubic_data->t_last_cong = ticks;
cubic_data->K = 0;
}
/*
* The mean RTT is used to best reflect the equations in
* the I-D. Using min_rtt in the tf_cwnd calculation