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

[Jamal Hadi Salim <jhs@mojatatu.com>]

On Fri, Jan 27, 2023 at 6:02 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 1/27/23 9:04 PM, Jamal Hadi Salim wrote:
> > On Fri, Jan 27, 2023 at 1:26 PM Jiri Pirko <jiri@resnulli.us> wrote:
> >> Fri, Jan 27, 2023 at 12:30:22AM CET, kuba@kernel.org wrote:
> >>> On Tue, 24 Jan 2023 12:03:46 -0500 Jamal Hadi Salim wrote:
> >>>> There have been many discussions and meetings since about 2015 in regards to
> >>>> P4 over TC and now that the market has chosen P4 as the datapath specification
> >>>> lingua franca
> >>>
> >>> Which market?
> >>>

[..]
> >
> > Our rule in TC is: _if you want to offload using TC you must have a
> > s/w equivalent_.
> > We enforced this rule multiple times (as you know).
> > P4TC has a sw equivalent to whatever the hardware would do. We are pushing that
> > first. Regardless, it has value on its own merit:
> > I can run P4 equivalent in s/w in a scriptable (as in no compilation
> > in the same spirit as u32 and pedit),
>
> `62001 insertions(+), 45 deletions(-)` and more to come for a software
> datapath which in the end no-one will use (assuming you'll have the hw
> offloads) is a pretty heavy lift..

I am not sure i fully parsed what you said - but the sw stands on its own
merit. The consumption of P4 specification is one - but ability to define
arbitrary pipelines without changing the kernel code (u32/pedit like, etc) is
of value.
Note (in case i misunderstood what you are saying):
As mentioned there is commitment to support; its clean standalone and
can be compiled out
and even when compiled in has no effect on the rest of the code performance
or otherwise.

> imo the layer of abstraction is wrong
> here as Stan hinted. What if tomorrow P4 programming language is not the
> 'lingua franca' anymore and something else comes along? Then all of it is
> still baked into uapi instead of having a generic/versatile intermediate
> later.

Match-action pipeline as an approach to defining datapaths is what we
implement here.
It is what P4 defines. I dont think P4 covers everything that is
needed under the shining sun
but a lot of effort has gone into standardizing common things. And if
there are gaps we fill them.
That is a solid, well understood way to build hardware and sw (TC has
been around all these
years implementing that paradigm). So that is the intended abstraction
being implemented.
The interface is designed to be scriptable to remove the burden of
making kernel (and btw user space
as well to iproute2) changes for new processing functions (whether in
s/w or hardware).

cheers,
jamal