Date: Tue, 17 Nov 2020 08:11:17 +0000 (UTC) From: Richard Scheffenegger <rscheff@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r367753 - stable/12/sys/netinet/cc Message-ID: <202011170811.0AH8BHKs078511@repo.freebsd.org>
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Author: rscheff Date: Tue Nov 17 08:11:17 2020 New Revision: 367753 URL: https://svnweb.freebsd.org/changeset/base/367753 Log: MFC r367008: TCP Cubic: improve reaction to (and rollback from) RTO fix compliancy issue of CUBIC RTO handling according to RFC8312 section 4.7 add CUBIC CC_RTO_ERR handling Submitted by: chengc_netapp.com Reviewed by: rrs, tuexen, rscheff Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D26808 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 Tue Nov 17 08:03:49 2020 (r367752) +++ stable/12/sys/netinet/cc/cc_cubic.c Tue Nov 17 08:11:17 2020 (r367753) @@ -78,7 +78,7 @@ static void cubic_conn_init(struct cc_var *ccv); static int cubic_mod_init(void); static void cubic_post_recovery(struct cc_var *ccv); static void cubic_record_rtt(struct cc_var *ccv); -static void cubic_ssthresh_update(struct cc_var *ccv); +static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg); static void cubic_after_idle(struct cc_var *ccv); struct cubic { @@ -90,19 +90,28 @@ struct cubic { unsigned long max_cwnd; /* cwnd at the previous congestion event. */ unsigned long prev_max_cwnd; + /* A copy of prev_max_cwnd. Used for CC_RTO_ERR */ + unsigned long prev_max_cwnd_cp; /* various flags */ uint32_t flags; #define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */ #define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */ #define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */ +#define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */ /* Minimum observed rtt in ticks. */ int min_rtt_ticks; /* Mean observed rtt between congestion epochs. */ int mean_rtt_ticks; /* ACKs since last congestion event. */ int epoch_ack_count; - /* Time of last congestion event in ticks. */ + /* Timestamp (in ticks) of arriving in congestion avoidance from last + * congestion event. + */ int t_last_cong; + /* Timestamp (in ticks) of a previous congestion event. Used for + * CC_RTO_ERR. + */ + int t_last_cong_prev; }; static MALLOC_DEFINE(M_CUBIC, "cubic data", @@ -142,7 +151,14 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type) cubic_data->flags |= CUBICFLAG_IN_SLOWSTART; newreno_cc_algo.ack_received(ccv, type); } else { - if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | + if ((cubic_data->flags & CUBICFLAG_RTO_EVENT) && + (cubic_data->flags & CUBICFLAG_IN_SLOWSTART)) { + /* RFC8312 Section 4.7 */ + cubic_data->flags &= ~(CUBICFLAG_RTO_EVENT | + CUBICFLAG_IN_SLOWSTART); + cubic_data->max_cwnd = CCV(ccv, snd_cwnd); + cubic_data->K = 0; + } else if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | CUBICFLAG_IN_APPLIMIT)) { cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART | CUBICFLAG_IN_APPLIMIT); @@ -274,10 +290,10 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type) case CC_NDUPACK: if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { - cubic_ssthresh_update(ccv); + cubic_ssthresh_update(ccv, mss); cubic_data->flags |= CUBICFLAG_CONG_EVENT; cubic_data->t_last_cong = ticks; - cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); + cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); } ENTER_RECOVERY(CCV(ccv, t_flags)); } @@ -285,37 +301,35 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type) case CC_ECN: if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { - cubic_ssthresh_update(ccv); + cubic_ssthresh_update(ccv, mss); cubic_data->flags |= CUBICFLAG_CONG_EVENT; cubic_data->t_last_cong = ticks; - cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); + cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); ENTER_CONGRECOVERY(CCV(ccv, t_flags)); } break; case CC_RTO: - CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd), - CCV(ccv, snd_cwnd)) / 2 / mss, - 2) * mss; - CCV(ccv, snd_cwnd) = mss; - /* - * Grab the current time and record it so we know when the - * most recent congestion event was. Only record it when the - * 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)); + /* RFC8312 Section 4.7 */ + if (CCV(ccv, t_rxtshift) == 1) { + cubic_data->t_last_cong_prev = cubic_data->t_last_cong; + cubic_data->prev_max_cwnd_cp = cubic_data->prev_max_cwnd; } + cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT; + cubic_data->prev_max_cwnd = cubic_data->max_cwnd; + CCV(ccv, snd_ssthresh) = ((uint64_t)CCV(ccv, snd_cwnd) * + CUBIC_BETA) >> CUBIC_SHIFT; + CCV(ccv, snd_cwnd) = mss; break; + + case CC_RTO_ERR: + cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT); + cubic_data->max_cwnd = cubic_data->prev_max_cwnd; + cubic_data->prev_max_cwnd = cubic_data->prev_max_cwnd_cp; + cubic_data->t_last_cong = cubic_data->t_last_cong_prev; + cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); + break; } } @@ -437,7 +451,7 @@ cubic_record_rtt(struct cc_var *ccv) * Update the ssthresh in the event of congestion. */ static void -cubic_ssthresh_update(struct cc_var *ccv) +cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg) { struct cubic *cubic_data; uint32_t ssthresh; @@ -467,7 +481,7 @@ cubic_ssthresh_update(struct cc_var *ccv) ssthresh = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; } - CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * CCV(ccv, t_maxseg)); + CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg); }
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