[RFC] ethdev: datapath-focused meter actions, continue

[Alexander Kozyrev]

On Wed, May 18, 2022 12:51 Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>:
> I'm sorry, I'm not sure that I can take part in tomorrow meeting, so,
> I'd like to drop my thoughts on the topic via E-mail.

Thank you for taking some time and reviewing this RFC.

> Existing "meter" object which pulls profile and policy together allows
> do apply metering in one flow-based lookup for different flows.
> I.e. we can route absolutely different flows to one meter object to
> share metering counters. When we know meter ID for a flow, everything
> becomes simple - just get corresponding metering counters, apply it and
> do actions based on color. Yes, it is not flexible, but very simple. As
> I understand the configuration model enforces to define actions for all
> colors.

Yes, and what I propose is the flexible version of Meters where both
profiles and policies can be used separately. But flexibility comes with
a price of taking care of both of them separately as well, of course.

> A new model, if I'm not mistaken, will require three flow-based lookups:
>   1. To assign a TAG based on flow fields (to handle different flows in
> one meter)
>   2. To do metering for packets with a TAG
>   3. To find actions based on color
> Of course, (2) and (3) are done in existing model with meter ID, but
> here it is a generic flow-based lookups with extra matching criteria.
> Yes, it is true that it gives extra flexibility, but everything has its
> price.

We don't need to assign a TAG. I used the TAG as example on how we can
combine color matching with any other item matching.  Model stays the same.
You still do color marking with a meter and find actions based on a color.

> Theoretically old model could be expressed using new one (and,
> therefore, supported on old HW), but it is a bit tricky and raises many
> questions on how to handle it correctly in all cases. E.g. if a TAG is
> the only pattern in non-zero table and used for meter+jump actions only,
> it could be associated with meter ID.
> Above jump table specified after meter action could be associated with a
> policy ID. If action for a color is not specified in a table, it should
> be drop by default.

Yes, old model can be expressed via new API and new model can be
simulated with the old API. Efficiency and performance is the key.

> Indirect actions or action templates could help to do meter profile job
> - define profile in single place.

True, meter color marking may be used for meter sharing, for example.

> To sum up, since some HW could support the flexibility provided by
> suggested flow API items/actions. I see no reason to block it. Solution
> looks good from flow API design point of view.

Thank you.

> May be I'm missing something since I'm not expert in QoS and have no
> hands-on experience with meters in DPDK.
> 
> Andrew.