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

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Message-ID: <628a909d-1090-dc62-a730-fd9514079218@uls.co.za>
Date:   Fri, 1 Apr 2022 13:36:44 +0200
From:   Jaco Kroon <jaco@....co.za>
To:     Eric Dumazet <edumazet@...gle.com>
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

Hi Eric,

On 2022/04/01 02:54, Eric Dumazet wrote:
> 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.
Sorry, I understand TCP itself a bit, but I've given up trying to
understand the various schedulers a long time ago and am just using the
defaults that the kernel provides.  How do I check what I'm using, and
how can I change that?  What is recommended at this stage?
>
>
> 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
Ok, instead of starting with bisect, if I can reproduce in dev I'll use
this one first.

Kind Regards,
Jaco