[P4-discuss] (Help) Questions about blog "Improving Network Monitoring and Management with Programmable Data Planes"

Nate Foster jnfoster at cs.cornell.edu
Fri Jan 13 01:48:18 EST 2017


That's correct. P4's constructs for describing parsers, actions, tables,
and controls specify the core packet-processing functionality of the
switch.

In P4-14, some of the information you mention may be available as metadata
on some targets, but this is not mandated by the language specification.

P4-16 offers support for "architectures" and "extern functions." In
principle, one could define an architecture that exposes this information
and makes it available to the rest of the program through extern functions
with standard names. Then, any target that implements this architecture
would need to supply implementations for these functions.

-N

On Thu, Jan 12, 2017 at 10:40 AM, Libin Liu <liulibinsdu at gmail.com> wrote:

> Thanks, Andy. I don't understand that.
> You mean the P4 language can not guarantee those information, that is the
> barefoot switch ASIC which can already provide those information, e.g.,
> link utilization, queue depth, link latency? Thanks a lot.
>
> Best Regards,
> Libin
>
> 在 2017年1月13日,02:19,Andy Fingerhut <andy.fingerhut at gmail.com> 写道:
>
> My understanding is that whether a particular P4 target architecture
> supports visibility into such information about the queue depths and link
> utilizations can vary from P4 target to P4 target.  It is not guaranteed by
> the language to be available for all of them (nor even are the presence of
> queues guaranteed by the language, e.g. programmable NIC cards might not
> have any).
>
> I don't have access to details about current P4 capable switch ASICs, but
> I would guess that Barefoot's Tofino ASIC family gives such visibility.
>
> Andy
>
> On Thu, Jan 12, 2017 at 5:20 AM, Libin Liu <liulibinsdu at gmail.com> wrote:
>
>> Dear P4 developers,
>>
>> Hope this email finds you in the best of your health and spirits.
>> I am very interested in this blog. Can P4 switch already directly measure
>> the link utilization, link latency, and switch queue? If so, where can I
>> get the open source code about the module of measuring link utilization,
>> link latency, and switch queue? Thanks a lot for your help.
>>
>> Best Regards,
>> Libin
>>
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>
>
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