netdev - Re: [PATCH net-next v3 4/4] net: gro: move L3 flush checks to tcp_gro

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Date: Sat, 9 Mar 2024 16:41:46 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Richard Gobert <richardbgobert@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	willemdebruijn.kernel@...il.com, dsahern@...nel.org, xeb@...l.ru, 
	shuah@...nel.org, idosch@...dia.com, razor@...ckwall.org, amcohen@...dia.com, 
	petrm@...dia.com, jbenc@...hat.com, bpoirier@...dia.com, b.galvani@...il.com, 
	gavinl@...dia.com, liujian56@...wei.com, horms@...nel.org, 
	linyunsheng@...wei.com, therbert@...gle.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/4] net: gro: move L3 flush checks to tcp_gro_receive

On Sat, Mar 9, 2024 at 4:35 PM Richard Gobert <richardbgobert@...il.com> wrote:
>
> {inet,ipv6}_gro_receive functions perform flush checks (ttl, flags,
> iph->id, ...) against all packets in a loop. These flush checks are
> relevant only to tcp flows, and as such they're used to determine whether
> the packets can be merged later in tcp_gro_receive.
>
> These checks are not relevant to UDP packets.

I do not think this claim is true.

Incoming packets  ->  GRO -> GSO -> forwarded packets

The {GRO,GSO} step must be transparent, GRO is not LRO.