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

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Date:   Sat, 2 Apr 2022 09:32:24 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Jaco Kroon <jaco@....co.za>, Florian Westphal <fw@...len.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>, Wei Wang <weiwan@...gle.com>
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

On Sat, Apr 2, 2022 at 9:29 AM Neal Cardwell <ncardwell@...gle.com> wrote:
>
> FWIW those log entries indicate netfilter on the mail client machine
> dropping consecutive outbound skbs with 2*MSS of payload. So that
> explains the large consecutive losses of client data packets to the
> e-mail server. That seems to confirm my earlier hunch that those drops
> of consecutive client data packets "do not look like normal congestive
> packet loss".


This also explains why we have all these tiny 2-MSS packets in the pcap.

Under normal conditions, autocorking should kick in, allowing TCP to
build bigger TSO packets.