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From:   Dave Taht <dave.taht@gmail.com>
Date:   Thu, 12 Dec 2019 20:42:04 -0800
Message-ID: <CAA93jw7N34xs6HxutbArLABz4DWBy9kAWV-sxT8VqMkVSCne1w@mail.gmail.com>
Subject: Re: [Make-wifi-fast] debugging TCP stalls on high-speed wifi
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Simon Barber <simon@superduper.net>,
        Make-Wifi-fast <make-wifi-fast@lists.bufferbloat.net>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Neal Cardwell <ncardwell@google.com>,
        Netdev <netdev@vger.kernel.org>
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On Thu, Dec 12, 2019 at 5:46 PM Eric Dumazet <eric.dumazet@gmail.com> wrote=
:
>
>
>
> On 12/12/19 4:59 PM, Simon Barber wrote:
> > I=E2=80=99m currently adding ACK thinning to Linux=E2=80=99s GRO code. =
Quite a simple addition given the way that code works.
> >
> > Simon
> >
> >
>
> Please don't.
>
> 1) It will not help since many NIC  do not use GRO.
>
> 2) This does not help if you receive one ACK per NIC interrupt, which is =
quite common.

Packets accumulate in the wifi device and driver, if that's the bottleneck.

>
> 3) This breaks GRO transparency.
>
> 4) TCP can implement this in a more effective/controlled way,
>    since the peer know a lot more flow characteristics.
>
> Middle-box should not try to make TCP better, they usually break things.

I generally have more hope for open source attempts at this than other
means. And there isn't much left
in TCP that will change in the future; it is an ossified protocol.

802.11n, at least, has a problem fitting many packets into an
aggregate. Sending less packets is a win
in multiple ways:

A) Improves bi-directional throughput
B) Reduces the size of the receivers txop (and retries) - the client
is also often running at a lower rate than
the ap.
C) Delivers the most current ack, sooner

When further transiting an aqm that uses random numbers, it hits the
right packet sooner, also.

I welcome experimentation in this area.


--=20
Make Music, Not War

Dave T=C3=A4ht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-435-0729