Author: rscheff Date: Thu Sep 3 08:45:21 2020 New Revision: 365294 URL: https://svnweb.freebsd.org/changeset/base/365294
Log: MFC r364197: TCP Cubic: Have Fast Convergence Heuristic work for ECN, and align concave region The Cubic concave region was not aligned nicely for the very first exit from slow start, where a 50% cwnd reduction is done instead of the normal 30%. This addresses an issue, where a short line-rate burst could result from that sudden jump of cwnd. In addition, the Fast Convergence Heuristic has been expanded to work also with ECN induced congestion response. Submitted by: chengc_netapp.com Reported by: chengc_netapp.com Reviewed by: tuexen (mentor), rgrimes (mentor) Approved by: tuexen (mentor), rgrimes (mentor) MFC after: 3 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D25976 Modified: stable/12/sys/netinet/cc/cc_cubic.c Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/netinet/cc/cc_cubic.c ============================================================================== --- stable/12/sys/netinet/cc/cc_cubic.c Thu Sep 3 08:41:38 2020 (r365293) +++ stable/12/sys/netinet/cc/cc_cubic.c Thu Sep 3 08:45:21 2020 (r365294) @@ -286,8 +286,7 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type) if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { cubic_ssthresh_update(ccv); cubic_data->flags |= CUBICFLAG_CONG_EVENT; - cubic_data->prev_max_cwnd = cubic_data->max_cwnd; - cubic_data->max_cwnd = CCV(ccv, snd_cwnd); + cubic_data->t_last_cong = ticks; cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); } ENTER_RECOVERY(CCV(ccv, t_flags)); @@ -298,8 +297,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type) if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { cubic_ssthresh_update(ccv); cubic_data->flags |= CUBICFLAG_CONG_EVENT; - cubic_data->prev_max_cwnd = cubic_data->max_cwnd; - cubic_data->max_cwnd = CCV(ccv, snd_cwnd); cubic_data->t_last_cong = ticks; cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); @@ -361,11 +358,6 @@ cubic_post_recovery(struct cc_var *ccv) cubic_data = ccv->cc_data; pipe = 0; - /* Fast convergence heuristic. */ - if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd) - cubic_data->max_cwnd = (cubic_data->max_cwnd * CUBIC_FC_FACTOR) - >> CUBIC_SHIFT; - if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { /* * If inflight data is less than ssthresh, set cwnd @@ -392,7 +384,6 @@ cubic_post_recovery(struct cc_var *ccv) CUBIC_BETA) >> CUBIC_SHIFT, 2 * CCV(ccv, t_maxseg)); } - cubic_data->t_last_cong = ticks; /* Calculate the average RTT between congestion epochs. */ if (cubic_data->epoch_ack_count > 0 && @@ -403,7 +394,6 @@ cubic_post_recovery(struct cc_var *ccv) cubic_data->epoch_ack_count = 0; cubic_data->sum_rtt_ticks = 0; - cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); } /* @@ -457,18 +447,32 @@ cubic_ssthresh_update(struct cc_var *ccv) { struct cubic *cubic_data; uint32_t ssthresh; + uint32_t cwnd; cubic_data = ccv->cc_data; + cwnd = CCV(ccv, snd_cwnd); + /* Fast convergence heuristic. */ + if (cwnd < cubic_data->max_cwnd) { + cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT; + } + cubic_data->prev_max_cwnd = cubic_data->max_cwnd; + cubic_data->max_cwnd = cwnd; + /* - * On the first congestion event, set ssthresh to cwnd * 0.5, on - * subsequent congestion events, set it to cwnd * beta. + * On the first congestion event, set ssthresh to cwnd * 0.5 + * and reduce max_cwnd to cwnd * beta. This aligns the cubic concave + * region appropriately. On subsequent congestion events, set + * ssthresh to cwnd * beta. */ - if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) - ssthresh = CCV(ccv, snd_cwnd) >> 1; - else - ssthresh = ((uint64_t)CCV(ccv, snd_cwnd) * + if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) { + ssthresh = cwnd >> 1; + cubic_data->max_cwnd = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; + } else { + ssthresh = ((uint64_t)cwnd * + CUBIC_BETA) >> CUBIC_SHIFT; + } CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * CCV(ccv, t_maxseg)); } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
