Re: TCP and BBR: reproducibly low cwnd and bandwidth

On Fri, Feb 16, 2018 at 11:43 AM, Eric Dumazet [off-list ref] wrote:

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

quoted

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,

Eric raises a good question: bare metal vs VMs.

Oleksandr, your first email mentioned KVM VMs and virtio NICs. Your
second e-mail did not seem to mention if those results were for bare
metal or a VM scenario: can you please clarify the details on your
second set of tests?

Thanks!