From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleksandr Natalenko <oleksandr@natalenko.name>
Subject: Re: TCP and BBR: reproducibly low cwnd and bandwidth
Date: Sat, 17 Feb 2018 00:06:23 +0100
Message-ID: <2829276.7yTBvbjqgd@natalenko.name>
References: <1697118.nv5eASg0nx@natalenko.name> <CANn89iJ_P4AUKEVAzWYWd-4rk336zftDXSe_nCNxU3O7NqwrNQ@mail.gmail.com> <1518821435.55655.6.camel@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Cc: Eric Dumazet <edumazet@google.com>,
        Neal Cardwell <ncardwell@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Netdev <netdev@vger.kernel.org>,
        Yuchung Cheng <ycheng@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Jerry Chu <hkchu@google.com>, Dave Taht <dave.taht@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Return-path: <netdev-owner@vger.kernel.org>
Received: from vulcan.natalenko.name ([104.207.131.136]:57192 "EHLO
        vulcan.natalenko.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751020AbeBPXGZ (ORCPT
        <rfc822;netdev@vger.kernel.org>); Fri, 16 Feb 2018 18:06:25 -0500
In-Reply-To: <1518821435.55655.6.camel@gmail.com>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

On p=E1tek 16. =FAnora 2018 23:50:35 CET Eric Dumazet wrote:
> /* snip */
> If you use
>=20
> tcptrace -R test_s2c.pcap
> xplot.org d2c_rtt.xpl
>=20
> Then you'll see plenty of suspect 40ms rtt samples.

That's odd. Even the way how they look uniformly.

> It looks like receiver misses wakeups for some reason,
> and only the TCP delayed ACK timer is helping.
>=20
> So it does not look like a sender side issue to me.

To make things even more complicated, I've disabled sg on the server, leavi=
ng=20
it enabled on the client:

client to server flow: 935 Mbits/sec
server to client flow: 72.5 Mbits/sec

So still, to me it looks like a sender issue. No?