netdev - Re: [PATCH 0/6] tcp: support preloading data on a listening socket

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Message-ID: <CADVnQymxsOGLnUfurhDLXNUaK4gpaYm2zTDEWRxy8JPqH6O6vg@mail.gmail.com>
Date: Fri, 16 May 2025 14:19:26 -0400
From: Neal Cardwell <ncardwell@...gle.com>
To: Jeremy Harris <jgh@...m.org>
Cc: netdev@...r.kernel.org, linux-api@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH 0/6] tcp: support preloading data on a listening socket

On Fri, May 16, 2025 at 11:55 AM Jeremy Harris <jgh@...m.org> wrote:
>
> Support write to a listen TCP socket, for immediate
> transmission on passive connection establishments.
>
> On a normal connection transmission is triggered by the receipt of
> the 3rd-ack. On a fastopen (with accepted cookie) connection the data
> is sent in the synack packet.
>
> The data preload is done using a sendmsg with a newly-defined flag
> (MSG_PRELOAD); the amount of data limited to a single linear sk_buff.
> Note that this definition is the last-but-two bit available if "int"
> is 32 bits.

Can you please add a bit more context, like:

+ What is the motivating use case? (Accelerating Exim?) Is this
targeted for connections using encryption (like TLS/SSL), or just
plain-text connections?

+ What are the exact performance improvements you are seeing in your
benchmarks that (a) motivate this, and (b) justify any performance
impact on the TCP stack?

+ Regarding "Support write to a listen TCP socket, for immediate
transmission on passive connection establishments.": can you please
make it explicitly clear whether the data written to the listening
socket is saved and transmitted on all future successful passive
sockets that are created for the listener, or is just transmitted on
the next connection that is created?

thanks,
neal