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

[Andrew Rybchenko]

Hi all,

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.

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.

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.

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.

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

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.

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

Andrew.