netdev - Re: [PATCH net-next RFC 00/20] Introducing P4TC

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Message-ID: <CAM0EoMk8e4rR5tX5giC-ggu_h-y32hLN=ENZ=-A+XqjvnbCYpQ@mail.gmail.com>
Date:   Mon, 30 Jan 2023 19:26:05 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     "Singhai, Anjali" <anjali.singhai@...el.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jamal Hadi Salim <hadi@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Willem de Bruijn <willemb@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel@...atatu.com" <kernel@...atatu.com>,
        "Chatterjee, Deb" <deb.chatterjee@...el.com>,
        "Limaye, Namrata" <namrata.limaye@...el.com>,
        "khalidm@...dia.com" <khalidm@...dia.com>,
        "tom@...anda.io" <tom@...anda.io>,
        "pratyush@...anda.io" <pratyush@...anda.io>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "vladbu@...dia.com" <vladbu@...dia.com>,
        "simon.horman@...igine.com" <simon.horman@...igine.com>,
        "stefanc@...vell.com" <stefanc@...vell.com>,
        "seong.kim@....com" <seong.kim@....com>,
        "mattyk@...dia.com" <mattyk@...dia.com>,
        "Daly, Dan" <dan.daly@...el.com>,
        "Fingerhut, John Andy" <john.andy.fingerhut@...el.com>
Subject: Re: [PATCH net-next RFC 00/20] Introducing P4TC

On Mon, Jan 30, 2023 at 7:06 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> Singhai, Anjali wrote:
> > Devlink is only for downloading the vendor specific compiler output for a P4 program and for teaching the driver about the names of runtime P4 object as to how they map onto the HW. This helps with the Initial definition of the Dataplane.
> >
> > Devlink is NOT for the runtime programming of the Dataplane, that has to go through the P4TC block for anybody to deploy a programmable dataplane between the HW and the SW and have some flows that are in HW and some in SW or some processing HW and some in SW. ndo_setup_tc framework and support in the drivers will give us the hooks to program the HW match-action entries.
> > Please explain through ebpf model how do I program the HW at runtime?
> >
> > Thanks
> > Anjali
> >
>
> Didn't see this as it was top posted but, the answer is you don't program
> hardware the ebpf when your underlying target is a MAT.
>
> Use devlink for the runtime programming as well, its there to program
> hardware. This "Devlink is NOT for the runtime programming" is
> just an artificate of the design here which I disagree with and it feels
> like many other folks also disagree.
>

We are going to need strong justification to use devlink for
programming the  binary interface to begin with - see the driver
models discussion. And let me get this clear: you are suggesting we
use it for runtime and redo all that tc ndo and associated infra?

cheers,
jamal

> Also if you have some flows going to SW you want to use the most
> performant option you have which would be XDP-BPF at the moment in a
> standard linux box or maybe af-xdp. So in these cases you should look
> to divide your P4 pipeline between XDP and HW. Sure you can say
> performance doesn't matter for my use case, but surely it does for
> some things and anyways you have the performant thing already built
> so just use it.
> Thanks,
> John