[Coin] Fwd: The Future of P4, Revisited

[Marie-Jose Montpetit <[e-mail]>]

Interesting article for out community.

mjm

Marie-José Montpetit, Ph.D.
[e-mail]



From: Larry Peterson from Systems Approach <[e-mail]>
<[e-mail]>
Reply: Larry Peterson from Systems Approach
<reply+1zsws7&rqag0&&[e-mail]>
<reply+1zsws7&rqag0&&[e-mail]>
Date: May 15, 2023 at 3:55:52 AM
To: [e-mail] <[e-mail]> <[e-mail]>
Subject:  The Future of P4, Revisited

The P4 Workshop was a couple weeks ago, and as General Chair, I went into
it with a fair amount of trepidation. My concern was that Intel’s
announcement earlier this year that they’re cancelling development of the
Tofino 3 switching chip would have a chilling effect, not only on the
Workshop, but also on the future of P4. That concern has been voiced in
several forums
 ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌
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‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌
Open in app
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or online
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The Future of P4, Revisited
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Larry Peterson
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May 15
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The P4 workshop has now been chaired by both co-founders of Systems
Approach, but this year the P4 landscape has shifted again with Intel’s
announcement that Tofino 3, its flagship P4-powered switching chip, would
not go ahead. There is much more to P4 than Tofino, however, as we explore
in this week’s newsletter.
------------------------------

The P4 Workshop
<https://substack.com/redirect/4b87822a-70c6-4ffa-864a-45637b26909c?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
was a couple weeks ago, and as General Chair, I went into it with a fair
amount of trepidation. My concern was that Intel’s announcement
<https://substack.com/redirect/a0831b60-fff8-4ded-88c7-f3e6ef7e1e54?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
earlier this year that they’re cancelling development of the Tofino 3
switching chip would have a chilling effect, not only on the Workshop, but
also on the future of P4. That concern has been voiced in several forums,
including SIGCOMM’s Slack workspace
<https://substack.com/redirect/300dcab9-6056-4c82-9627-1e08ea449b0e?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>,
with members of the P4 Advisory Board
<https://substack.com/redirect/2fcc130d-cf74-4d68-be4e-d531cbb379b4?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
making reassuring pronouncements in various settings. (See for example,
Nick McKeown’s post to the P4 Forum
<https://substack.com/redirect/b0f9bc57-686d-4962-8676-c234ebcbd12f?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>,
and Nick along with Nate Foster and Jennifer Rexford discussing the future
of Network Programmability on The Networking Channel
<https://substack.com/redirect/f2016908-8afb-4538-be3d-5d0e6aab0b3c?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
).

I won’t try to give a point-by-point replay of what Nick, Nate, and Jen and
others have been saying, except to observe that at a high level it can be
summarized as follows:

*Programmable Networks  >>  P4 Language  >>  Tofino Switching Chip*

They point out, for example, that Tofino is just one of many interesting
backend targets for P4 programs (SmartNICs
<https://substack.com/redirect/f5d04cdb-5915-42ab-9904-a20c38eeab33?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
and IPUs
<https://substack.com/redirect/a0ddc803-4ea3-4248-96a1-bdc33f86cd15?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
being the next “big deal”) and P4 is one of many tools being used to inject
functionality into the end-to-end network path (DPDK and eBPF being two
active projects that people are integrating with P4). Ultimately, the value
of programmability comes from having visibility and control over the
network, and there are many complementary approaches to making that happen.
With that background, I do have three takeaways from what turned out to be
an interesting and vibrant two days at the P4 Workshop (despite my initial
concerns).

First, we’re often so focused on P4 as a tool to program the forwarding
pipeline that we forget the other half of its value proposition: It also
provides a way to specify the behavior of a pipeline (independent of how
that pipeline is implemented). We talk about this idea, and the value of
being able to auto-generate the Control API, in the P4 chapter of our SDN
Book
<https://substack.com/redirect/4b87822a-70c6-4ffa-864a-45637b26909c?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>.
Rob Sherwood made a similar argument
<https://substack.com/redirect/2442a19b-b82c-410c-8692-f50b89733875?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
at the P4 Workshop. It is now becoming a reality as companies like Google
are starting to use such behavioral definitions as a Hardware Abstraction
Layer (see Parveen Patel’s Keynote
<https://substack.com/redirect/e656a164-3fef-497b-9628-ffeb700108af?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
at the Workshop). This makes me hopeful that we are rapidly approaching the
day when a P4 program (plus the generated P4RT interface) will become the
standard way network providers specify their requirements to network
vendors, and proposed new features (whether proprietary or standard) will
be specified by a P4 program (potentially augmenting the intuition and
design rationale presented in an RFC).

*As an aside, I couldn’t help but notice the similarities between the
architecture Parveen described and the way P4 has been used to program the
forwarding plane of the 5G Mobile Core
<https://substack.com/redirect/64e4cac9-e6fd-4652-8e36-09f50ff1305c?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>.
Both include a P4-based “abstract forwarding model” that’s independent of
the underlying implementation details*.

Second, it is common to divide forwarding pipelines into “programmable”
versus “fixed function”, but this glosses over what might be the more
important distinction: whether the pipeline is *open* or *closed*. Even
“fixed function” pipelines are increasingly flexible–it’s just a question
of how restrictive the vendor is in who they allow to make changes. This
restriction may have the biggest impact on researchers who want to
experiment with a new feature (especially ones that do not yet have a
proven market), but maybe less so in the commercial world where incentives
to make changes are (arguably) well-defined. Using P4 as the “spec
language” (as I just outlined) has the potential to accelerate the process
on the commercial side. On the research side, there is a strong argument in
favor of using Tofino 2 to demonstrate the feasibility and value of new
ideas (12.8 Tb/s still makes for a credible Proof-of-Concept), and
repeating the refrain yet again, P4-as-spec makes for a compelling tech
transfer story. If that were to happen, it would be interesting to see how
vendors and chip designers adapt to reduce their spec-to-hardware
implementation overhead. I would argue that programmable forwarding planes
have a time-to-market advantage even for closed solutions.

Third, our focus on quantifiable metrics makes it easy to forget about the
less quantifiable aspects of programmability. At its core, P4 is a
programming language that does a good job of abstracting the essence of a
packet forwarding pipeline. It is enormously impressive that a P4 program
can be compiled onto a PISA-based
<https://substack.com/redirect/01cfb256-04e7-49f8-9600-55e1471955b8?j=eyJ1IjoicnFhZzAifQ.CwdsLjQyIcRXfYRGUucLsXfrvggM3KKa9Z1jxtXNWH0>
switching chip that has the same performance, die area, cost, and power
consumption of a fixed-function ASIC (and that equivalency was probably
necessary for P4 to be taken seriously), but hitting that quantifiable mark
is not sufficient. Well-designed languages are software tools that bring
clarity to the intellectual challenge of programming. For me, the biggest
“aha” moment of the Workshop was when Chris Sommers (long-time P4
contributor and new co-Chair of the API Working Group) started rattling off
all the functions he’d been involved in writing in P4, and remarking on how
natural P4 makes that process. There is certainly room to add new language
features as P4 expands its domain to include SmartNICs and IPUs—as Chris
and the other WG chairs are now pursuing—but having an existing target to
evolve is a great position to be in.

One common thread that weaves its way through these three takeaways is that
Intel’s cancellation of the Tofino 3 chip is a potentially helpful forcing
function: The P4 community has to demonstrate the value of the language
without being buttressed by ever-improving performance numbers that have
more to do with 7nm semiconductor technology than anything networking
people have done. I saw a lot of evidence that exactly that is happening at
last month’s workshop. The march to programmable networks is inevitable (in
my view), and I’m still optimistic about the role P4 will play a central
role.

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