netdev - Re: [PATCH net-next 09/10] net: renesas: rswitch: add simple l3 routing

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Message-ID: <4c93ea95-a601-4cf5-ba92-a5a0e672ab62@lunn.ch>
Date: Fri, 7 Nov 2025 14:46:44 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Michael Dege <michael.dege@...esas.com>
Cc: Nikita Yushchenko <nikita.yoush@...entembedded.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	"niklas.soderlund" <niklas.soderlund@...natech.se>,
	Paul Barker <paul@...rker.dev>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"magnus.damm" <magnus.damm@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH net-next 09/10] net: renesas: rswitch: add simple l3
 routing

> > But, there is a more interesting question about this patchset (that actually stopped me from
> > submitting
> > it when it was originally developed).
> >
> > What do people thing about the entire approach used to detect streams to offload?
> >
> > The situation is:
> > - hardware is capable of doing L3 routing, with some (limited) packet update capabilities - rewrite
> > DST
> > MAC, decrease TTL,
> > - there is interest to use that, because software L3 routing even at 1Gbps consumes significant CPU
> > load, and for 5Gbps will likely not keep the speed at all (we did not have hw to try),
> > - but - given the capabilities of hw are incomparably weaker than capabilities of linux networking,
> > which approach to take to detect streams for offloading?
> >
> > Second question - how exactly to get the routing decision from the kernel stack, to apply it in
> > hardware? I was not able to find any existing implementations of something similar...

You should probably look at how the mellanox switch does this. It is
kind of the reference implementation. The sparx5 and prestera might
have something, i don't remember their capabilities.

Some of the mediatek devices also do interesting things with flows,
but that is more for NAT, not necessarily L3 routing.

	Andrew