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 23:50:55 +0100
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Cc: Neal Cardwell <ncardwell@google.com>,
        Eric Dumazet <eric.dumazet@gmail.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 <edumazet@google.com>
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Hi.

On p=E1tek 16. =FAnora 2018 21:54:05 CET Eric Dumazet wrote:
> /* snip */
> Something fishy really :
> /* snip */
> Not only the receiver suddenly adds a 25 ms delay, but also note that
> it acknowledges all prior segments (ack 112949), but with a wrong ecr
> value ( 2327043753 )
> instead of 2327043759
> /* snip */

Eric has encouraged me to look closer at what's there in the ethtool, and I=
've=20
just had a free time to play with it. I've found out that enabling scatter-
gather (ethtool -K enp3s0 sg on, it is disabled by default on both hosts)=20
brings the throughput back to normal even with BBR+fq_codel.

Whyyyy? What's the deal BBR has with sg?

Oleksandr