netdev - Re: [PATCH net-next 0/3] tcp: better deal with delayed TX completions

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Date:   Fri, 12 Mar 2021 14:09:19 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Neil Spring <ntspring@...com>
Subject: Re: [PATCH net-next 0/3] tcp: better deal with delayed TX completions

On Fri, Mar 12, 2021 at 2:05 PM Yuchung Cheng <ycheng@...gle.com> wrote:
>
> On Fri, Mar 12, 2021 at 10:18 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Thu, 11 Mar 2021 12:35:03 -0800 Eric Dumazet wrote:
> > > From: Eric Dumazet <edumazet@...gle.com>
> > >
> > > Jakub and Neil reported an increase of RTO timers whenever
> > > TX completions are delayed a bit more (by increasing
> > > NIC TX coalescing parameters)
> > >
> > > While problems have been there forever, second patch might
> > > introduce some regressions so I prefer not backport
> > > them to stable releases before things settle.
> > >
> > > Many thanks to FB team for their help and tests.
> > >
> > > Few packetdrill tests need to be changed to reflect
> > > the improvements brought by this series.
> >
> > FWIW I run some workloads with this for a day and looks good:
> >
> > Tested-by: Jakub Kicinski <kuba@...nel.org>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> Thank you Eric for fixing the bug.

The series looks good to me as well.

Re this one:
-               WARN_ON(tp->retrans_out != 0);
+               WARN_ON(tp->retrans_out != 0 && !tp->syn_data);

it seems a little unfortunate to lose the power of this WARN_ON for
the lifetime of TFO connections, but I do not have a better idea. :-)

thanks,
neal