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: Fri, 16 Feb 2018 18:37:08 +0100
Message-ID: <18081951.d6t0IUddpn@natalenko.name>
References: <1697118.nv5eASg0nx@natalenko.name> <2189487.nPhU5NAnbi@natalenko.name> <CANn89iKqSkh=3D5-arubZkYdVTbb6C=OR5vK0sMDoO6S3A0GeQ@mail.gmail.com>
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Cc: "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Neal Cardwell <ncardwell@google.com>,
        Yuchung Cheng <ycheng@google.com>,
        Van Jacobson <vanj@google.com>, Jerry Chu <hkchu@google.com>
To: Eric Dumazet <edumazet@google.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <CANn89iKqSkh=3D5-arubZkYdVTbb6C=OR5vK0sMDoO6S3A0GeQ@mail.gmail.com>
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Hi.

On p=E1tek 16. =FAnora 2018 17:25:58 CET Eric Dumazet wrote:
> The way TCP pacing works, it defaults to internal pacing using a hint
> stored in the socket.
>=20
> If you change the qdisc while flow is alive, result could be unexpected.

I don't change a qdisc while flow is alive. Either the VM is completely=20
restarted, or iperf3 is restarted on both sides.

> (TCP socket remembers that one FQ was supposed to handle the pacing)
>=20
> What results do you have if you use standard pfifo_fast ?

Almost the same as with fq_codel (see my previous email with numbers).

> I am asking because TCP pacing relies on High resolution timers, and
> that might be weak on your VM.

Also, I've switched to measuring things on a real HW only (also see previou=
s=20
email with numbers).

Thanks.

Regards,
  Oleksandr