[Mpi3-subsetting] agenda for subsetting kickoff telecon ww09

[Torsten Hoefler]

Hi,
>    Present: Leonid Meyerguz (Microsoft), Rich Graham (ORNL), Richard Barrett
>    (ORNL), Torsten Hoefler (ISU), Alexander Supalov (Intel)
just for the record, it's "IU" not "ISU" :-)

>    - Scope of the effort
>      - Rich
>        - Minimum subset consistent with the rest of MPI, for
>    performance/memory footprint optimization
>        - Danger of splitting MPI, hence against optional features in the
>    standard
I back that (danger of optional features for portability). I'd propose
to split the current standard into mostly self-contained subsets that
have clearly defined interfaces to the rest of the standard. Note: this
only defines logical interfaces, that does *not* define how those things
are to be implemented. This makes it easier to understand the standard
and have separate (portable) libraries for the subsets, it does not
influence optimization possibilities by implementing everything in a
monolithic block (i.e., central progress). 

>        - Both blocking & nonblocking belong to the core
>      - Torsten
>        - Some collectives may go into selectable subsets
I see three subsets: blocking colls, non-blocking colls and topological
colls (maybe also blocking / non-blocking).

>        - MPI_ANY_SOURCE considered harmful
I'd like to add datatypes and heterogeneity to this list (with regards
to performance). Alexander mentioned the dynamics. I think we should
have a lit of items ready that could influence optimization
possibilities significanty if they were to be announced by the user
before he can use them. That would give another strong argument for the
subsetting.

Best,
  Torsten


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