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Differential D24817

DCTCP: update alpha only once after loss recovery.
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Authored by rscheff on May 12 2020, 6:43 AM.
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tuexen
rrs
jtl
thj
rgrimes
cc
Group Reviewers
transport
Commits
rS361808: MFC rS361348: DCTCP: update alpha only once after loss recovery.
rS361348: DCTCP: update alpha only once after loss recovery.
Summary

During code inspection and testing of DCTCP in mixed
loss and ECN marking scenarios, it was found that the alpha
value of DCTCP is updated twice during windows expiriencing loss.

While RFC8257 is silent on the interaction between loss
recovery and updates of alpha, updating it one additional time
with an effective ECN marking rate of 0 reduces the effect of
ECN marks due to the lower alpha value. This in turn may result
in an overall higher loss rate than necessary.

Reported-by: Cheng Cui

Test Plan

A packetdrill script with the expected evolution
of cwnd is provided.

Diff Detail

Lint
Lint Passed
Unit
No Test Coverage
Build Status
Buildable 31040
Build 28746: arc lint + arc unit

Event Timeline

rscheff created this revision.May 12 2020, 6:43 AM
Herald added a subscriber: melifaro. · View Herald TranscriptMay 12 2020, 6:43 AM
rscheff requested review of this revision.May 12 2020, 6:43 AM
Harbormaster completed remote builds in B31040: Diff 71676.May 12 2020, 6:43 AM
rscheff added a comment.May 12 2020, 7:31 AM

Attached the packetdrill script to validate the evolution of cwnd under loss and ecn for dctcp.

dctcp-post-recovery.pkt3 KBDownload

cc accepted this revision.May 12 2020, 6:49 PM

Looks good. Thanks for picking this up.

This revision is now accepted and ready to land.May 12 2020, 6:49 PM
rrs accepted this revision.May 21 2020, 2:19 PM
tuexen accepted this revision.May 21 2020, 2:20 PM
Closed by commit rS361348: DCTCP: update alpha only once after loss recovery. (authored by rscheff). · Explain WhyMay 21 2020, 9:43 PM
This revision was automatically updated to reflect the committed changes.
rscheff added a commit: rS361348: DCTCP: update alpha only once after loss recovery..
Herald added a subscriber: imp. · View Herald TranscriptMay 21 2020, 9:43 PM
rscheff added a commit: rS361808: MFC rS361348: DCTCP: update alpha only once after loss recovery..Jun 4 2020, 9:02 PM
Herald added a reviewer: transport. · View Herald TranscriptJun 4 2020, 9:02 PM

Revision Contents
Changeset List

PathSize
sys/
netinet/
cc/
6 lines

Diff 71676

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sys/netinet/cc/cc_dctcp.c

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