"WITH_INFO" review across the collective API

[tonyskjellum]

Problem

Make sure all the functions have variants "WITH_INFO" for which this makes sense.

Proposal

Check the collective API, starting with the GRAPH/CART APIs below, to see where WITH_INFO is missing but needed; add such APIs. In some cases, we might deprecate the prior meaning of the info argument instead (TBD per API).

Changes to the Text

MPI_GRAPH_CREATE_WITH_INFO
The "non-dist" graph constructor should be deprecated in favour of the newer (and better) "dist" version(s). Every call to MPI_GRAPH_CREATE can be legally and 'simply' replaced with a call to MPI_DIST_GRAPH_CREATE.

MPI_GRAPH_CREATE requires that each process passes the full (global) communication graph to the call. This limits the scalability of this constructor. With the distributed graph interface, the communication graph is specified in a fully distributed fashion.

In the absence of a proposal to deprecate MPI_GRAPH_CREATE (and thereby obviate the need to maintain/improve it), adding an MPI_INFO argument is one of the advisable changes/improvements.

MPI_CART_CREATE_WITH_INFO
The proposed cartesian topology "with info" constructor seems like a good addition but should probably be part of a more general change to add an MPI_INFO argument to all object constructors that don't already have one. For example, MPI_COMM_SPLIT_WITH_INFO makes a lot of sense too.

Impact on Implementations

Incremental APIs will need to be added; these are analogous to existing APIs and mechanisms to manage WITH_INFO already exist in other parts of the API.

Impact on Users

Describe the changes that will impact users here.

References

Issue #80 must be cross-correlated; See also Issue #85.

[tonyskjellum]

We have plenty of work for Austin, and we need to understand the plans and outcomes of Ticket #80 to pursue this ticket efficiently. So I am going to mark its goal as for Barcelona, not Austin. Let's discuss in the WG in Austin.