netdev - Re: TCP and BBR: reproducibly low cwnd and bandwidth

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Date:   Fri, 16 Feb 2018 08:43:11 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        "David S. Miller" <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Jerry Chu <hkchu@...gle.com>
Subject: Re: TCP and BBR: reproducibly low cwnd and bandwidth

On Fri, Feb 16, 2018 at 8:33 AM, Neal Cardwell <ncardwell@...gle.com> 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