09 Feb 2017 Hangout Notes

rrs@ mentions that they now have a “black box recorder” which is done by jtl@. This uses a set probes to collect data over time. It collects data in pcap form t so that you can look at it tcpdump. It can either stream data or dump data following a signal. jtl@ will put up a review soonish. gnn@ wonders if much can be done with DTrace.

BBR has been handed over to the production team and will be off by default in the NF kernels, but can be turned on via a socket option. The performance is looking good in their testing. rrs@ wants to get this into their transport lab for testing. One issue remains the CPU utilization of the callout system. rrs@ will move BBR to using the pacing infrastructure as it has a lower CPU overhead than the callout system.

People need to review https://reviews.freebsd.org/D9356 which glebius has put up for review. This splits listen sockets from data transport sockets.

rrs@ points out that if you are always in sequence and not having loss you will grow your window but will never tell the peer. He says he will make a patch for review.

hiren@ is working with lstewart@ on what's broken with the fast recovery fix. The fix from a few months ago to not revert to 1MSS seems to result in a higher level of retransmits.

gnn@ asks if tuexen@ is ready to push his changes to tcp-testsuite

gnn@ will kick off a conversation with Neal at Google and tuexen@ about upstreaming to the main repo

rstone@ asks for review of https://reviews.freebsd.org/D9465 . bz@ suggests taking some of the UTO spares.

tuexen@ asks what happens in IPv6 when we process a “packet too big” ICMP error. On IPv4 the host cache is updated. bz@ will send the things he knows about this directly to tuexen@

rstone@ points out that clearing the SRTT after 3 retransmits makes debugging harder. rstone@ will put up phabricator on this topic.

tuexen@ asks about this review https://reviews.freebsd.org/D9475 which addresses an issue with very small receive buffers.