Page MenuHomeFreeBSD
Differential D56535

tcp: Align PRR implementation with RFC 9937
Needs ReviewPublic
Actions

Authored by mohnishhemanthkumar_gmail.com on Apr 20 2026, 5:46 PM.
Tags
Referenced Files
Unknown Object (File)
Thu, May 14, 2:30 AM
Unknown Object (File)
Wed, May 13, 6:42 PM
Unknown Object (File)
Wed, May 13, 6:42 PM
Unknown Object (File)
Wed, May 13, 4:18 PM
Unknown Object (File)
Wed, May 13, 4:18 PM
Unknown Object (File)
Mon, May 11, 12:24 PM
Unknown Object (File)
Wed, May 6, 2:24 PM
Unknown Object (File)
Tue, May 5, 10:19 AM
View All 23 Files
Subscribers
glebius
imp
melifaro

Details

Reviewers
rscheff
Group Reviewers
transport
Summary

The main changes implemented in tcp_do_prr_ack() (in tcp_input.c) are:

  • Early return when no new data is delivered (del_data = 0). (RFC 9937 6.2)
  • Switching from PRR-CRB to PRR-SSRB only when both SND.UNA advances and no further loss is indicated. (RFC 9937 4)
  • Accounting for sequence ranges SACKed before entering recovery in RecoverFS calculation. (RFC 9937 4)
  • Force a fast retransmit upon entering recovery when prr_out is 0 AND SndCnt is 0. (RFC 9937 4)
  • Set cwnd to ssthresh post recovery. (RFC 9937 4)
Test Plan

packetdrill_prr.pkt2 KBDownload

Detailed Report: https://docs.google.com/document/d/16OeBZ8Zp0D5umq_asm8Dl6grINuLwn1I8baoncuhTF0/edit?tab=t.0

Diff Detail

Repository
rG FreeBSD src repository
Lint
Lint Skipped
Unit
Tests Skipped

Event Timeline

mohnishhemanthkumar_gmail.com created this revision.Apr 20 2026, 5:46 PM
mohnishhemanthkumar_gmail.com created this object with edit policy "mohnishhemanthkumar_gmail.com (Mohnish Hemanth Kumar)".
Herald added a reviewer: transport. · View Herald TranscriptApr 20 2026, 5:46 PM
Herald added subscribers: glebius, melifaro, imp. · View Herald Transcript
mohnishhemanthkumar_gmail.com requested review of this revision.Apr 20 2026, 5:46 PM
mohnishhemanthkumar_gmail.com attached a referenced file: F153364136: packetdrill_prr.pkt. (Show Details)
mohnishhemanthkumar_gmail.com edited the summary of this revision. (Show Details)Apr 20 2026, 5:50 PM
mohnishhemanthkumar_gmail.com retitled this revision from Align PRR implementation with RFC9937 to tcp: Align PRR implementation with RFC 9937.Apr 20 2026, 6:43 PM
rscheff added a comment.Apr 21 2026, 10:28 AM

Thanks,
I'll discuss this with all the transport committers in the next call.

First reading looks good, have to check the packetdrill differences too.

Revision Contents
Changeset List

PathSize
sys/
netinet/
45 lines

Diff 175927

View Options

sys/netinet/tcp_input.c

Loading...