Author: rscheff Date: Wed Jul 1 09:35:33 2020 New Revision: 362832 URL: https://svnweb.freebsd.org/changeset/base/362832
Log: MFC r362006: Prevent TCP Cubic to abruptly increase cwnd after app-limited Cubic calculates the new cwnd based on absolute time elapsed since the start of an epoch. A cubic epoch is started on congestion events, or once the congestion avoidance phase is started, after slow-start has completed. When a sender is application limited for an extended amount of time and subsequently a larger volume of data becomes ready for sending, Cubic recalculates cwnd with a lingering cubic epoch. This recalculation of the cwnd can induce a massive increase in cwnd, causing a burst of data to be sent at line rate by the sender. This adds a flag to reset the cubic epoch once a session transitions from app-limited to cwnd-limited to prevent the above effect. Reviewed by: chengc_netapp.com, tuexen (mentor) Approved by: tuexen (mentor), rgrimes (mentor) MFC after: 3 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D25065 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 Wed Jul 1 09:32:17 2020 (r362831) +++ stable/12/sys/netinet/cc/cc_cubic.c Wed Jul 1 09:35:33 2020 (r362832) @@ -92,6 +92,7 @@ struct cubic { 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 */ /* Minimum observed rtt in ticks. */ int min_rtt_ticks; /* Mean observed rtt between congestion epochs. */ @@ -143,8 +144,10 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type) } else { ticks_since_cong = ticks - cubic_data->t_last_cong; - if (cubic_data->flags & CUBICFLAG_IN_SLOWSTART) { - cubic_data->flags &= ~CUBICFLAG_IN_SLOWSTART; + 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; } @@ -197,6 +200,9 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type) cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) cubic_data->max_cwnd = CCV(ccv, snd_cwnd); } + } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && + !(ccv->flags & CCF_CWND_LIMITED)) { + cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; } } _______________________________________________ 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"
