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

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Date:   Tue, 31 Jan 2023 05:30:10 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     John Fastabend <john.fastabend@...il.com>,
        "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>,
        "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 Tue, Jan 31, 2023 at 5:27 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Mon, Jan 30, 2023 at 11:12 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Mon, 30 Jan 2023 19:26:05 -0500 Jamal Hadi Salim wrote:
> > > > 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
> >
> > We may disagree on direction, but we should agree status quo / reality.
> >
> > What John described is what we suggested to Intel to do (2+ years ago),
> > and what is already implemented upstream. Grep for DDP.
> >
>
> I went back and looked at the email threads - I hope i got the right
> one from 2020.
>
> Note, there are two paths in P4TC:
> DDP loading via devlink is equivalent to loading the P4 binary for the hardware.
> That is one of the 3 (and currently most popular) driver interfaces
> suggested. Some of that drew

Sorry didnt finish my thought here, wanted to say: The loading of the
P4 binary over devlink drew (to some people) suspicion it is going to
be used for loading kernel bypass.

cheers,
jamal

> Second is runtime which is via standard TC. John's proposal is
> equivalent to suggesting moving the flower interface Devlink. That is
> not the same as loading the config.
>
> > IIRC my opinion back then was that unless kernel has any use for
> > whatever the configuration exposes - we should stay out of it.
>
> It does for runtime and the tc infra already takes care of that. The
> cover letter says:
>
> "...one can be more explicit and specify "skip_sw" or "skip_hw" to either
> offload the entry (if a NIC or switch driver is capable) or make it purely run
> entirely in the kernel or in a cooperative mode between kernel and user space."
>
> cheers,
> jamal