PSA Meeting Minutes Nov 15, 2017

Attendees:

• AndyF, Tom, Han, Chris, Calin
• online: AndyK, Samar, James Coole, Antonin, Joe Tardo

Agenda

• Bridged metadata (Han, Andy) 45 min:

  • https://github.com/p4lang/p4-spec/issues/404
  • Proposal for metadata packing and unpacking https://github.com/p4lang/p4-spec/issues/453 We would really like to bring this issue closer to resolution. Please read and think about the example program attached https://github.com/p4lang/p4-spec/issues/453#issuecomment-341327037, in terms of programmer convenience, and writing a compiler to do it.

• Action Profiles (Samar) 15 min:

  • Added max_groups attribute to action selector https://github.com/p4lang/p4-spec/pull/449
  • Fungibility of action selector size https://github.com/p4lang/p4-spec/issues/456
  • Document interaction between direct counters/meters and action profile/selector https://github.com/p4lang/p4-spec/issues/466

• Naming (Calin) 15 min:

  • PSA table property names https://github.com/p4lang/p4-spec/pull/481
  • Consistent naming conventions https://github.com/p4lang/p4-spec/issues/483

• Miscellaneous (all) 15 min:

  • State of direct meters and counters when entries are added and removed https://github.com/p4lang/p4-spec/issues/359
  • Should InternetChecksum() extern be guaranteed initialized as if clear() was called? https://github.com/p4lang/p4-spec/issues/458
  • Is drop allowed in egress? (only remaining issue is I think creating an example suggested by Samar Abdi) https://github.com/p4lang/p4-spec/issues/444
  • Using virtual functions to specify action chosen in action_selector https://github.com/p4lang/p4-spec/issues/446
  • Document effect of multiple pipelines on PSA https://github.com/p4lang/p4-spec/issues/353

Discussion

Bridged metadata

• handling parameters
  • clear semantics
  • usability
    • lots of parameters
    • union type for struct in the language (P4_14 tagged union type)
  • what happens when the structs are mis-used?
    • how much compiler support we need to make this safe(er)
    • optimizations
      • overlaying fields
      • assigning to fields that are undefined
  • extern functions that returns the type of packet (resubmit(), normal(), clone()) for conditions that should be checked
  • guard the access to structs in the deparser
  • digest is still an extern, everything else is based on the pack/unpack
• AI: Andy to add to the example the guards
• AI: Andy to write up on the metadata initialization
• AI: Han to re-write the clone/recirc/resubmit sections based on this proposal

Action profiles

• Liveness: watch port in OpenFlow
  • is this really part of the architecture? No
  • is this something that P4 can handle? Chris: P4 can express the functionality of having tables that react on port failures, but it is not really part of the architecture
  • port management - micro-control-plane functionality
  • extern to determine port status to build a fast local controller
    • is this a table that's updated by a local controller continuously?
    • it should be callable multiple times
  • P4runtime API for fail-over?
    • platform management, sort of outside P4
    • Tom: handled fully between P4Runtime and the embedded software
    • Antonin: thinks that the watch-bit can be fully implemented at the P4Runtime API level with new APIs for the action selectors
      • annotations in the P4 program to enable the feature
      • annotations in the P4Runtime to specify the ports
  • SDN controller view: see the PSA as the switch that has some
• AI: Andy to review the P4Runtime proposal for handling this and then we'll discuss what needs to be done for PSA.

Draft release for Nov 10

• Andy and Calin to merge all outstanding PRs before the weekend
• Weekend and next week will be spend in editorial mode
• Calin to add a Known Issue section