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

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Date:   Fri, 16 Feb 2018 11:45:56 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...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 11:43 AM, Eric Dumazet <edumazet@...gle.com> wrote:
>
> 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,

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!