linux-kernel - Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

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Message-ID: <CANn89i+6LCWOZahAi_vPf9H=SKw-4vdMTj5T0dYsp1Se4g9-yw@mail.gmail.com>
Date:   Thu, 31 Mar 2022 17:54:58 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jaco Kroon <jaco@....co.za>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

On Thu, Mar 31, 2022 at 5:41 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Mar 31, 2022 at 5:33 PM Jaco Kroon <jaco@....co.za> wrote:
>
> > I'll deploy same on a dev host we've got in the coming week and start a
> > bisect process.
>
> Thanks, this will definitely help.

One thing I noticed in your pcap is a good amount of drops, as if
Hystart was not able to stop slow-start before the drops are
happening.

TFO with one less RTT at connection establishment could be the trigger.

If you are still using cubic, please try to revert.


commit 4e1fddc98d2585ddd4792b5e44433dcee7ece001
Author: Eric Dumazet <edumazet@...gle.com>
Date:   Tue Nov 23 12:25:35 2021 -0800

    tcp_cubic: fix spurious Hystart ACK train detections for
not-cwnd-limited flows