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

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Date:   Tue, 31 Jan 2023 15:38:33 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jamal Hadi Salim <hadi@...atatu.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        kernel@...atatu.com, deb.chatterjee@...el.com,
        anjali.singhai@...el.com, namrata.limaye@...el.com,
        khalidm@...dia.com, tom@...anda.io, pratyush@...anda.io,
        xiyou.wangcong@...il.com, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, vladbu@...dia.com, simon.horman@...igine.com,
        stefanc@...vell.com, seong.kim@....com, mattyk@...dia.com,
        dan.daly@...el.com, john.andy.fingerhut@...el.com
Subject: Re: [PATCH net-next RFC 00/20] Introducing P4TC

Tue, Jan 31, 2023 at 01:17:14PM CET, toke@...hat.com wrote:
>Jamal Hadi Salim <jhs@...atatu.com> writes:
>
>> Toke, i dont think i have managed to get across that there is an
>> "autonomous" control built into the kernel. It is not just things that
>> come across netlink. It's about the whole infra.
>
>I'm not disputing the need for the TC infra to configure the pipelines
>and their relationship in the hardware. I'm saying that your
>implementation *of the SW path* is the wrong approach and it would be
>better done by using BPF (not talking about the existing TC-BPF,
>either).
>
>It's a bit hard to know your thinking for sure here, since your patch
>series doesn't include any of the offload control bits. But from the
>slides and your hints in this series, AFAICT, the flow goes something
>like:
>
>hw_pipeline_id = devlink_program_hardware(dev, p4_compiled_blob);
>sw_pipeline_id = `tc p4template create ...` (etc, this is generated by P4C)
>
>tc_act = tc_act_create(hw_pipeline_id, sw_pipeline_id)
>
>which will turn into something like:
>
>struct p4_cls_offload ofl = {
>  .classid = classid,
>  .pipeline_id = hw_pipeline_id
>};
>
>if (check_sw_and_hw_equivalence(hw_pipeline_id, sw_pipeline_id)) /* some magic check here */
>  return -EINVAL;
>
>netdev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_P4, &ofl);
>
>
>I.e, all that's being passed to the hardware is the ID of the
>pre-programmed pipeline, because that programming is going to be
>out-of-band via devlink anyway.
>
>In which case, you could just as well replace the above:
>
>sw_pipeline_id = `tc p4template create ...` (etc, this is generated by P4C)
>
>with
>
>sw_pipeline_id = bpf_prog_load(BPF_PROG_TYPE_P4TC, "my_obj_file.o"); /* my_obj_file is created by P4c */
>
>and achieve exactly the same.
>
>Having all the P4 data types and concepts exist inside the kernel
>*might* make sense if the kernel could then translate those into the
>hardware representations and manage their lifecycle in a uniform way.
>But as far as I can tell from the slides and what you've been saying in
>this thread that's not going to be possible anyway, so why do you need
>anything more granular than the pipeline ID?

Toke, I understand what what you describe above is applicable for the P4
program instantiation (pipeline definition).

What is the suggestion for the actual "rule insertions" ? Would it make
sense to use TC iface (Jamal's or similar) to insert rules to both BPF SW
path and offloaded HW path?


>
>-Toke
>