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| author | Richard Scheffenegger <rscheff@FreeBSD.org> | 2020-06-10 07:32:02 +0000 |
|---|---|---|
| committer | Richard Scheffenegger <rscheff@FreeBSD.org> | 2020-06-10 07:32:02 +0000 |
| commit | 2fda0a6f3aa9c3190bcab3c682dd51df110c1a2b (patch) | |
| tree | 9822f5997f0b5e351fbac95e6376d4a1c56a981b /sys/netinet/cc | |
| parent | 2b2c6d69191b689af79a1210f97b13719eb487a4 (diff) | |
| download | src-2fda0a6f3aa9c3190bcab3c682dd51df110c1a2b.tar.gz src-2fda0a6f3aa9c3190bcab3c682dd51df110c1a2b.zip | |
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
Notes
Notes:
svn path=/head/; revision=362006
Diffstat (limited to 'sys/netinet/cc')
| -rw-r--r-- | sys/netinet/cc/cc_cubic.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c index 28e3d3c51649..cec5917e01b3 100644 --- a/sys/netinet/cc/cc_cubic.c +++ b/sys/netinet/cc/cc_cubic.c @@ -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; } } |