Notes 2020 10 29

MPI Forum Tools Meeting 2020-10-29

Participants

• Marc-Andre Hermanns
• Bengisu Elis
• Atul Kulkarni
• Bill Williams
• Chris Chambreau
• Wesley Bland Intel
• Joachim Protze
• Martin Schulz

Topcis

• Initialization a 2-phase process

  • Phase 1: Tools registeres with a name and pointer to init-function
    • By any means (e.g., constructor attribute) in arbitrary order
  • Phase 2: Env-Variable (e.g., QMPI_TOOLS=mpip:myfancecollectives:mpip) determines the order of initialization (and ordering in the stack)

• Tool interception calls should be allowed to be called after Init

  • Allow meta tools to intercept interception calls themselves

• Allow dynamic adding/removing of tools

  • need function to enforce tools to rebuild their internal "picture" of the stack
  • Use a callback for "tool has been added" and "tool has been removed"

• We currently don't have anything to query arbitrary members of the stack

  • Only myself and the next

• Context handling

  • QMPI_Context opaque handle

    • Internal information stored there
    • not tool specific but specific to the function you are calling
      • memory is managed by the mechanism that calls the next function in the stack

  • Contents

    • Function point to next function in the stack
    • Storage object provided by the tool during registration
    • calling address of the user code

  • Same context object is handed down the complete calling stack

    • Tool does not need to query it anymore
    • MPI manages the lifetime of the object

  • How to do the handling of the "last user function"

    • Stackwalking can be expensive
    • As it's part of the opaque object, we could add this info later