Date: Thu, 30 Apr 2020 11:11:28 +0000 (UTC) From: Richard Scheffenegger <rscheff@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r360491 - head/sys/netinet/cc Message-ID: <202004301111.03UBBS6i018668@repo.freebsd.org>
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Author: rscheff Date: Thu Apr 30 11:11:28 2020 New Revision: 360491 URL: https://svnweb.freebsd.org/changeset/base/360491 Log: Introduce a lower bound of 2 MSS to TCP Cubic. Running TCP Cubic together with ECN could end up reducing cwnd down to 1 byte, if the receiver continously sets the ECE flag, resulting in very poor transmission speeds. In line with RFC6582 App. B, a lower bound of 2 MSS is introduced, as well as a typecast to prevent any potential integer overflows during intermediate calculation steps of the adjusted cwnd. Reported by: Cheng Cui Reviewed by: tuexen (mentor) Approved by: tuexen (mentor) MFC after: 2 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D23353 Modified: head/sys/netinet/cc/cc_cubic.c Modified: head/sys/netinet/cc/cc_cubic.c ============================================================================== --- head/sys/netinet/cc/cc_cubic.c Thu Apr 30 06:34:34 2020 (r360490) +++ head/sys/netinet/cc/cc_cubic.c Thu Apr 30 11:11:28 2020 (r360491) @@ -366,8 +366,9 @@ cubic_post_recovery(struct cc_var *ccv) CCV(ccv, t_maxseg); else /* Update cwnd based on beta and adjusted max_cwnd. */ - CCV(ccv, snd_cwnd) = max(1, ((CUBIC_BETA * - cubic_data->max_cwnd) >> CUBIC_SHIFT)); + CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->max_cwnd * + CUBIC_BETA) >> CUBIC_SHIFT, + 2 * CCV(ccv, t_maxseg)); } cubic_data->t_last_cong = ticks; @@ -433,6 +434,7 @@ static void cubic_ssthresh_update(struct cc_var *ccv) { struct cubic *cubic_data; + uint32_t ssthresh; cubic_data = ccv->cc_data; @@ -441,10 +443,11 @@ cubic_ssthresh_update(struct cc_var *ccv) * subsequent congestion events, set it to cwnd * beta. */ if (cubic_data->num_cong_events == 0) - CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd) >> 1; + ssthresh = CCV(ccv, snd_cwnd) >> 1; else - CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) * + ssthresh = ((uint64_t)CCV(ccv, snd_cwnd) * CUBIC_BETA) >> CUBIC_SHIFT; + CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * CCV(ccv, t_maxseg)); }
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