• TransportProtocols
• 01May2025

Attendees

• cc@
• glebius@
• tuexen@
• thj@
• Peter Lei

• info@spmzt.net

Ongoing Short Term Projects

• At least for testing purposes (packetdrill) it would be good to have LRO support for tun interfaces. tuexen@ suggested to generalize LRO to not depend on an Ethernet header being present. gallatin@ prefers to not make the LRO code more complex, since it most likely will impact the performance. tuexen@ has implemented LRO support for the tap interfaces. packetdrill support will be committed soon.
• BBLog is missing a man page. tuexen@ will write one.
• tuexen@ will add tests for handling RST ACK segments in all states and test the base, RACK and BBR stack.

• D46056 fixes a bug when sending UDP packets. tuexen@ committed it and reverted it, since it broke two tests related to IPv6 socket options. tuexen@ will look into it.

• D46425 needs some review. rscheff@ and tuexen@ will review it.

• The sent too much is still there in CURRENT. kevans@ experienced it and was able to provide a BBLog file. tuexen@ created a reproducer and D49922 provides a fix.

• tuexen@ started a discussion about indicating ungraceful termination of TCP connections using the SO_LINGER option. glebius suggested to use the on_off as a bitfield to enable verbosity. It was also suggested to reach out to other developers of Linux, FreeBSD, and Windows. tuexen@ will do that.

• glebius@ is looking at the potential deadlock due to locking two inpcbs in different order.

• glebius@ wants feedback on D48921. markj@ is testing it with syzkaller.

• glebius@ announces that a patch is being tested that allows to initialize the socket buffer from the TCP hostcache. In addition, the TCP hostcache entries will be generated and updated every 4 RTTs.

• cc@ provides an update for TCP CUBIC in D49540 to get it aligned with RFC 9438. cc@ wants review and will do more testing. rscheff@ will reach out to Broadcom for feedback.

• D50099 is covering TCP in combination with anycast. Reviews would be nice.

• D50103 is dealing with the definition of structures being sent over the network. Reviews would be nice.

• tuexen@ suggested to replace the two TCP related rate limiters by a single one. tuexen@ will provide a patch for further discussion.

Ongoing Longer Term Projects

• Now the RACK and the BBR stack are compiled by default in head. The BBR and the RACK stack will continue to coexists. We discussed if the RACK stack could be made the default and what should drive this decision. tuexen@ will reach out to the mailing list to ask people to test the RACK stack and provide feedback. In January, we will look again at the decision process based on the feedback we got. Feedback received:
  • You need to compile in the TCPHPTS. It is a loadable module now, thanks to glebius@.
  • RACK is on the loopback interface slower than the base stack (CPU limited). olivier@ has a script to test combinations of stacks and CC modules.

  • A problem with RACK and pf, which couldn't be reproduced by olivier@. tuexen@ has an idea what is going wrong and will provide a patch to the reporter for testing.D43769 fixes this, but adds some instructions to the code path.

  • When using mbuf queueing, some dtrace static probes are missed. Fixed.
  • There is a performance regression by just loading the HPTS module. This is fixed.
• It was discussed that it would be a good idea to move the freebsd stack from ticks to micro seconds.

• rscheff@ is improving AccECN code: D36303. rrs@ will review it and implement it for the rack stack. Also the interaction between LRO and AccECN++ has to be taken into account. D42563 further adds the support of ACKofACK.

• D23230 is implementing ECN++. rrs@ will review it.

• tuexen@ wants to write a tool which dumps the BBLog information of a TCP endpoint from a life system or a core. Using kvm_read() has drawbacks as glebius@ pointed out, using a python kgdb script may be an alternative. An alternative is to write a python kgdb script which pumps data into tcplog_dumper. This would allow to minimize code duplication. glebius@ will try to work on this soon. thj@ has an initial implementation at tcplog_dumper.

• The handling on ECN with TSO by NICs was discussed. tuexen@ will add a configuration option for various Intel NICs to make the TSO behavior configurable, rscheff@ will make in the TCP stack configurable wether classical ECN or AccECN will use TSO. tuexen@ wants feedback on D44258 and D44259.

• rgrimes@ reports that FreeBSD using the default parameters can not saturate a Gigabit pipe with a delay used by recent access technologies. He is proposing to bump up some default values.

• glebius@ will re-activate D35199 which speeds up finding bugs.

• tuexen@ will add fast open tests to the FreeBSD testsuite. This might require some additional counters.
• gallatin@ will look into improving performance by moving things around in structures. This will reduce cache misses...

• cc@ wants review of D47130. Possible ways of breaking up tcp_do_segment() were discussed. No agreement was reached. cc@ will try several ways and bring the alternatives back for further discussion.

Next Meeting

15 May 2025 @ 1500 UTC using FreeBSDTCPCall