netdev - Re: [PATCH] tcp: allow the initial receive window to be greater than 64KiB

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Message-ID: <CANn89i+1aPNwGCP1Y+-nPxh4A_+t0JdOWorZHvXpRD_2OhjTMQ@mail.gmail.com>
Date:   Sun, 13 Feb 2022 11:29:20 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Tian Lan <Tian.Lan@...sigma.com>
Cc:     Tian Lan <tilan7663@...il.com>, netdev <netdev@...r.kernel.org>,
        Andrew Chester <Andrew.Chester@...sigma.com>
Subject: Re: [PATCH] tcp: allow the initial receive window to be greater than 64KiB

On Sun, Feb 13, 2022 at 11:26 AM Tian Lan <Tian.Lan@...sigma.com> wrote:
>
> > I suggest that you do not interpret things as " BPF_SOCK_OPS_RWND_INIT could exceed 64KiB"  because it can not.
>
> > If you really need to send more than 64KB in the first RTT, TCP is not a proper protocol.
>
> > 13d3b1ebe287 commit message should have been very clear about the 64K limitation.
>
> I'm not trying to make the sender to send more than 64Kib in the first RTT. The change will only make the sender to send more starting on the second RTT(after first ack received on the data). Instead of having the rcv_wnd to grow from 64Kib, the rcv_wnd can start from a much larger base value.
>
> Without the patch:
>
> RTT:                                1,                   2,                 3,  ...
> rcv_wnd:                64KiB,        192KiB,         576KiB,  ...

This is just fine, in accordance with what we expect.

>
> With the patch (assume rcv_wnd is set to 512KiB):
>
> RTT:                                1,                    2,                3,   ...
> rcv_wnd:                64KiB,    1.536MiB,    4.608MiB,  ...

This is not needed, unless you want to blast MB of data in the second RTT.

Please get IETF approval first.