netdev - Re: [Make-wifi-fast] debugging TCP stalls on high-speed wifi

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Message-ID: <34a05f62-8dd0-9ea0-2192-1da5bfe6d843@gmail.com>
Date:   Thu, 12 Dec 2019 17:46:55 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Simon Barber <simon@...erduper.net>,
        Dave Taht <dave.taht@...il.com>
Cc:     Make-Wifi-fast <make-wifi-fast@...ts.bufferbloat.net>,
        Johannes Berg <johannes@...solutions.net>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [Make-wifi-fast] debugging TCP stalls on high-speed wifi

On 12/12/19 4:59 PM, Simon Barber wrote:
> I’m currently adding ACK thinning to Linux’s 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.

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.