2020 10 19 webex

#10/19/20 webex notes

Attending: Martin Schulz, Howard Pritchard, Martin Schreiber, Dan Holmes

• Switch webex to zoom
• Discuss bubbles

Discuss switching from webex to zoom

We'll switch to using TUM zoom. Currently webex info is on a private wiki page - https://github.com/mpiwg-sessions/mpi-standard/wiki. Martin Schulz updated the wiki with the zoom info.

Bubbles

Resume from our discussion last week about coming to consensus on the most recent version of a process set.

Review a bit from last week. Use external RM (slurm, pmix, etc.) to ask for additional resources. Martin Schreiber worried about having to support multiple ways of requesting resources given multiple different RM implementations.

We resumed on slide entitled "Call 2: notified that MPI processes are present". Discuss option 1. Option 2 - async notification - raises the problem of how to register callback functions. Dan doesn't want to hide such an API inside MPI_T. MPI_RT had a notion of callbacks - Dan brings this up. Async notification - put it on the "slow" list that we had put together in the old slide deck - https://github.com/mpiwg-sessions/sessions-issues/wiki/2016-12-12-webex/2016-12-12-webex.pptx

Versioning discussion review. Work on issue 3 - consistency in communicator creation. Consensus on only outdated fail is best, or hide versioning inside MPI. But then how would app know something was changed - well could check for size changing form a previous call. A convenience function to go straight from a session to a communicator (using process set name) would be useful here? Discussing the problem of a shrinking process set - CommFromGroup fails if the groups came from different versions of a process set.

We could use pseudo code to illustrate topics in missing: versioning slide. Particularly need pscode for issue 3. Need to think about case of errors return verses having a error handler associated with the session.

TODOS:

• work on pseudo-code for the missing:versioning slide
• Howard add link to ompi prototype and test codes.
• Howard will send out notice of change in meeting location