LDWG Meeting minutes: March 5, 2018

Attendees

• Calin Cascaval (Barefoot)
• Mihai Budiu (VMware)
• James Coole (Cisco)
• Mario Baldi (Cisco)
• Andy Fingerhut (Cisco)
• Nate Foster (Cornell)
• Bo Liu (Delta Networks)
• Andy Keep (Cisco)
• Safaa Mahrach (University of Hassan)
• Nassar Noel (Delta Networks)
• Venkat Puellela (Broadcom)
• Milad Sharif (Barefoot)
• Chris Sommers (IXIA / Keysight)
• Han Wang (Barefoot)

Status and Announcements

• P4 Workshop announcement
• Version 1.1: new features until April leaving us ~2 months to finalize

Parser Value Sets

• Status: Preliminary implementation and a PR summarizing restrictions on where parser value sets can be used
• Questions:
  • How to specify the size?
  • Hard to specify resource requirements for different match types?
• Action items
  • Han to coordinate with P4 Runtime WG
  • Han to change size from annotation to constructor parameter
  • Andy Fingerhut to draft a summary of the issues

Optional and Named Parameters

• Status: Preliminary design with additional use cases
• Observation: dropping positional optional parameters reduces ambiguity
• Questions
  • How to treat “_” in type system? Not in favor of adding an “undefined” value.
  • Want to restrict to compile-time optional parameters.
• Action items:
  • Mihai: overload resolution
  • Calin: specification text

Virtual Functions

• Motivation:
  • Some applications need programmer-defined configuration for externs.
  • We already have experimental support in the compiler.
  • Example: action selectors in PSA
• Questions:
  • Unclear how to reference non-local variables.
  • Abstract method is never explicitly invoked so we can’t simply abstract over those variables.
• Action item:
  • { Milad, Chris, Mihai, Antonin }, to convene a smaller group to work on it.

Saturating Fields

• P4_14 had support for saturating fields but P4_16 does not
• Proposal is to add saturating_int and saturating_bit
• Counter-proposal a single polymorphic extern function that increments with saturating semantics; avoids complexities of language extension
• Counter-argument to counter-proposal: seems heavyweight to use.
• Action Items: Gather evidence of use cases and support on different targets.

Announcements

• Modularity sub-working group forming. Email Nate if you want to get involved.
• Next meeting: March 26; Andy F to host at Cisco