Differential D25746

Address unintended jump of calculated cwnd when leaving slowstart
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Authored by rscheff on Jul 20 2020, 4:56 PM.

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lstewart
cc
tuexen
jtl
rrs
rgrimes

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rS365293: MFC r364196: TCP Cubic: After leaving slowstart fix unintended cwnd jump.
rS364196: TCP Cubic: After leaving slowstart fix unintended cwnd jump.

Summary

D23655 addresses jumps of cubic cwnd due to outdated t_last_cong
data, but initializing K to zero introduced a different miscalculation,
where cwnd would suddenly jump to the recorded max_cwnd instead of
gradually increasing either using the tcp-friendly equation, or the
concave growth region.

Properly calculating K instead of resetting it to zero resolves this issue.

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rS FreeBSD src repository - subversion

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Event Timeline

rscheff created this revision.Jul 20 2020, 4:56 PM

Herald added a reviewer: transport. · View Herald TranscriptJul 20 2020, 4:56 PM

Herald added a subscriber: melifaro. · View Herald Transcript

rscheff requested review of this revision.Jul 20 2020, 4:56 PM

Harbormaster completed remote builds in B32442: Diff 74705.Jul 20 2020, 4:56 PM

calc ticks_since_cong properly

Harbormaster completed remote builds in B32443: Diff 74706.Jul 20 2020, 5:22 PM

tuexen accepted this revision.Jul 20 2020, 10:39 PM

This revision is now accepted and ready to land.Jul 20 2020, 10:39 PM

rgrimes accepted this revision.Jul 20 2020, 10:51 PM

record going out from slowstart at the earliest possible moment

This revision now requires review to proceed.Jul 20 2020, 11:09 PM

Harbormaster completed remote builds in B32450: Diff 74724.Jul 20 2020, 11:09 PM

tuexen accepted this revision.Jul 20 2020, 11:11 PM

This revision is now accepted and ready to land.Jul 20 2020, 11:11 PM

Tested with my results: https://github.com/ccui1000/freebsd-tcp/wiki/test-D25746

Other than the comment to complement, I have no issues about this change.

sys/netinet/cc/cc_cubic.c
140 ↗	(On Diff #74724)	Suggest complement the comment above this added condition.

This revision now requires changes to proceed.Jul 30 2020, 2:36 PM

rscheff mentioned this in D25976: TCP Cubic: Have Fast Convergence Heuristic work for ECN, and align concave region.Aug 6 2020, 3:20 PM

update comment to correctly describe conditionals

Harbormaster completed remote builds in B32829: Diff 75541.Aug 7 2020, 8:18 AM

tuexen accepted this revision.Aug 7 2020, 8:19 AM

Looks good. Thanks for picking this up.

This revision is now accepted and ready to land.Aug 7 2020, 1:58 PM

rgrimes accepted this revision.Aug 7 2020, 3:33 PM

Closed by commit rS364196: TCP Cubic: After leaving slowstart fix unintended cwnd jump. (authored by rscheff). · Explain WhyAug 13 2020, 4:39 PM

This revision was automatically updated to reflect the committed changes.

rscheff added a commit: rS364196: TCP Cubic: After leaving slowstart fix unintended cwnd jump..

Herald added a subscriber: imp. · View Herald TranscriptAug 13 2020, 4:39 PM

rscheff added a commit: rS365293: MFC r364196: TCP Cubic: After leaving slowstart fix unintended cwnd jump..Sep 3 2020, 8:42 AM

Revision Contents
Changeset List

Path

Size

head/

sys/

netinet/

cc/

24 lines

Diff 75795

head/sys/netinet/cc/cc_cubic.c

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