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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7409814.oObJlsYiIU@natalenko.name>
Date:   Fri, 16 Feb 2018 23:50:55 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "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>, Dave Taht <dave.taht@...il.com>
Subject: Re: TCP and BBR: reproducibly low cwnd and bandwidth

Hi.

On pátek 16. února 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 
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) 
brings the throughput back to normal even with BBR+fq_codel.

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

Oleksandr