[ofiwg] libfabric 2.0 discussion slides from today

[Hefty, Sean]

A couple of notes from the call:

There was general agreement that the overall objective (once re-written) is worthwhile:
Apps written to APIs that are common between 1.x and 2.x would work with both versions.

Apps written to new features would require a newer version of libfabric, same as today.

Specifics would determine whether we can meet that objective.  There was a proposal that APIs or features that are not implemented could be removed with the potential to bring back, maybe through an alternative API.  That doesn't mean those features aren't considered useful (because some are), but with no users, there's no need to constrain ourselves to the current API.

A point was raised that any helper APIs that may be introduced would need to work with 1.x and 2.x.  This could be handled by having helper APIs that are static inline functions.  An example helper API would be one that would allocate, configure (bind CQ, AV, etc.), and enable an EP.  These would be similar to the helper calls in the librdmacm.  Helper APIs are conceptual only, with no specific proposals on the table.

There was discussion on limiting how CQs may be bound to EPs, and at a more abstract level how to handle progress.  Progress differs between a full HW implementation, versus one needing SW protocol support.  This difference is visible to apps.  Further discussion will be deferred until we discuss what threading models we will want to support with 2.x.  A proposal to remove selective completion was rejected.

Without broad agreement on a specific update to the API, the current behavior would be maintained.

- Sean
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