netdev - Re: [PATCH net-next] net: mvpp2: increase MTU limit when XDP enabled

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Date:   Wed, 6 Jan 2021 19:34:55 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <kabel@...nel.org>
Cc:     Sven Auhagen <sven.auhagen@...eatech.de>, netdev@...r.kernel.org,
        davem@...emloft.net, Jakub Kicinski <kuba@...nel.org>,
        Matteo Croce <mcroce@...rosoft.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH net-next] net: mvpp2: increase MTU limit when XDP enabled

On Wed, Jan 06, 2021 at 01:32:05PM +0100, Marek Behún wrote:
> On Wed, 6 Jan 2021 12:56:08 +0100
> Marek Behún <kabel@...nel.org> wrote:
> 
> > I also to write a simple NAT masquerading program. I think XDP can
> > increase NAT throughput to 2.5gbps as well.
> 
> BTW currently if XDP modifies the packet, it has to modify the
> checksums accordingly. There is a helper for that even, bpf_csum_diff.
> 
> But many drivers can offload csum computation, mvneta and mvpp2 for
> example.

Hi Marek

It does require that the MAC is DSA aware. The Freescale FEC for
example cannot do such csum, because the DSA header confuses it, and
it cannot find the IP header, etc. So if you do look at a generic way
to implement this, you need the MAC driver to indicate it has the
needed support.

       Andrew