Notes 2020 10 08

MPI Forum Tools WG Meeting 2020-10-08

Participants

• Marc-Andre Hermanns
• Bengisu Elis
• Pouy Kousha
• Joachim Protze
• Bill Williams
• Michael Knobloch
• Sudheer Chunduri
• Wesley Bland
• Chris Chambreau

Topics

• void* context added every function call
• Replacing/Deprecating MPI_Pcontrol with QMPI?
• How does the MPI library communicator
• QMPI Context Handle
  • Could be storage of MPI internal information (e.g., return address to user code)
  • Could the layer in the stack be communicated through this?
  • When would such an object be allocated?
    • We might need a fresh one for each (concurrent) call into MPI
      • One for each thread in thread-local storage?
• Skipping elements of the tool stack
• Tool Registration
  • See Joachim's proposal
    • What is the difference between tool context and instance context?
      • Which is provided to the QMPI Wrapper?
      • Couldn't the instance context be part of the tool context (latter has a pointer to the former)
    • Why is context provided at tool registration and tool initialization?
  • Proposal:
    1. Tool registers (with name & pointer to init function)
       • Only the tool registration needs to be in an __attribute__((constructor)) function
    2. MPI library calls tool init function for each registered tool in the order specified in an environment variable
       • MPI library provides level in the stack to the tool
       • Should a tool instance have a unique ID as well?
         • Could be used/queried inside a wrapper to distinguish which instance a call is for
    3. Tools provides
• Should we allow tools to be "bad citizens" by skipping other tools in the stack?
  • It could be a feature?
  • Where is the difference between skipping and branching?