Re: TCP and BBR: reproducibly low cwnd and bandwidth

On Fri, Feb 16, 2018 at 8:33 AM, Neal Cardwell [off-list ref] wrote:

Oleksandr,

Thanks for the detailed report! Yes, this sounds like an issue in BBR. We
have not run into this one in our team, but we will try to work with you to
fix this.

Would you be able to take a sender-side tcpdump trace of the slow BBR
transfer ("v4.13 + BBR + fq_codel == Not OK")? Packet headers only would be
fine. Maybe something like:

  tcpdump -w /tmp/test.pcap -c1000000 -s 100 -i eth0 port $PORT

Thanks!
neal

On baremetal and using latest net tree, I get pretty normal results at
least, on 40Gbit NIC,
with pfifo_fast, fq and fq_codel.

# tc qd replace dev eth0 root fq
# ./super_netperf 1 -H lpaa24 -- -K cubic
  25627
# ./super_netperf 1 -H lpaa24 -- -K bbr
  25897
# tc qd replace dev eth0 root fq_codel
# ./super_netperf 1 -H lpaa24 -- -K cubic
  22246
# ./super_netperf 1 -H lpaa24 -- -K bbr
  25228
# tc qd replace dev eth0 root pfifo_fast
# ./super_netperf 1 -H lpaa24 -- -K cubic
  25454
# ./super_netperf 1 -H lpaa24 -- -K bbr
  25508