netdev - Re: [PATCH net-next v13 09/19] net: psp: update the TCP MSS to reflect PSP packet overhead

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Message-ID: <CANn89iLr0pk68y+tTgrxNCTY0HfiAAt+gtRd7K04wHsqqPoQ_w@mail.gmail.com>
Date: Wed, 17 Sep 2025 21:20:48 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Daniel Zahka <daniel.zahka@...il.com>
Cc: Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>, 
	Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, 
	Boris Pismenny <borisp@...dia.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, David Ahern <dsahern@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Patrisious Haddad <phaddad@...dia.com>, Raed Salem <raeds@...dia.com>, 
	Jianbo Liu <jianbol@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>, 
	Rahul Rameshbabu <rrameshbabu@...dia.com>, Stanislav Fomichev <sdf@...ichev.me>, 
	Toke Høiland-Jørgensen <toke@...hat.com>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, Kiran Kella <kiran.kella@...adcom.com>, 
	Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v13 09/19] net: psp: update the TCP MSS to
 reflect PSP packet overhead

On Tue, Sep 16, 2025 at 5:10 PM Daniel Zahka <daniel.zahka@...il.com> wrote:
>
> From: Jakub Kicinski <kuba@...nel.org>
>
> PSP eats 40B of header space. Adjust MSS appropriately.
>
> We can either modify tcp_mtu_to_mss() / tcp_mss_to_mtu()
> or reuse icsk_ext_hdr_len. The former option is more TCP
> specific and has runtime overhead. The latter is a bit
> of a hack as PSP is not an ext_hdr. If one squints hard
> enough, UDP encap is just a more practical version of
> IPv6 exthdr, so go with the latter. Happy to change.
>
> Reviewed-by: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Daniel Zahka <daniel.zahka@...il.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>