Date: Wed, 10 Jun 2020 07:32:03 +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: r362006 - head/sys/netinet/cc Message-ID: <202006100732.05A7W3JB058534@repo.freebsd.org>
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Author: rscheff Date: Wed Jun 10 07:32:02 2020 New Revision: 362006 URL: https://svnweb.freebsd.org/changeset/base/362006 Log: 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: head/sys/netinet/cc/cc_cubic.c Modified: head/sys/netinet/cc/cc_cubic.c ============================================================================== --- head/sys/netinet/cc/cc_cubic.c Wed Jun 10 05:01:00 2020 (r362005) +++ head/sys/netinet/cc/cc_cubic.c Wed Jun 10 07:32:02 2020 (r362006) @@ -94,6 +94,7 @@ 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. */ @@ -153,8 +154,10 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type) cubic_data->t_last_cong = ticks - INT_MAX; } - 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; } @@ -214,6 +217,9 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type) CCV(ccv, t_maxseg)); } } + } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && + !(ccv->flags & CCF_CWND_LIMITED)) { + cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; } }
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