[mpi-21] ABI: feature categories

[Greg Bronevetsky <bronevetsky1@xxxxxxxx>]

To clarify the debate surrounding the ABI 
proposal I've gone through Greg Lindahl's talk 
and broken the main points of the talk down into the following categories:
        User-MPI interactions
        Application-MPI interactions
        System-MPI interactions
As we've discussed, about morph layers address 
all the points under the "Application-MPI 
interactions" category. In other words, if we 
used morph layers we wouldn't need to standardize 
things like mpi.h. What's left are the User-MPI 
and System-MPI interactions. The question that I 
would like to put forward is: How useful are 
these? Most of the discussion I've heard recently 
focuses on Application-MPI interactions. If we 
can table this for the time being until morph 
layers can be evaluated, is there enough support 
to proceed with the rest of the proposal or is 
the Application-MPI interactions the core part? Please speak up.

User-MPI interactions
        ?mpistart? -- ?mpirun? with standard args
                Start over: ?mpistart? with standardized args
                Require features such as 
supporting pipes of stdin, stdout, error
                --batch and ?batch-wait to 
assist scripting in the presense of batch queues... noop if no queue sys
Application-MPI interactions
        Fully specify what's in <mpi.h> and ?mpif.h?
                Variably-sized items have to be nailed down
                MPI_Status must have fixed length
        Need a sane shared-library setup to avoid relinking
                I think this means we need 1 
base library instead of the usual chaos
                Implementers can dlopen() additional libs as needed
                Perhaps we can have a clever 
upward-compatible scheme for MPI 1 and MPI 2 libs
System-MPI interactions
        Fully specify startup and queue system interaction in a flexible way
                Queue sys handles creation of MPI processes
                Standard command-line for MPI 
process, with enough info to connect to the ? job?
                MPI implementation provides ? job? process; all
                MPI processes contact to coordinate.
                        ? job? process started by mpistart
                Queue sys ensures all MPI processes exit at end.
                I think this supports all 
existing queue systems and MPI implementations
        Specify environmental items so that most apps are portable
                Getenv / putenv: most 
implementations don't propagate env vars to ranks 
1+; few support using putenv to other processes.
                Cwd depends on batch system and sysadmin
                        2 choices: least common denominator, or query fns?
                Stack size. Usually painful for users to fix.
                stdin/stdout/stderr... oh, don't forget buffering...
                MPI-I/O.
                Actions before/after mpi_init/finalize

Greg Bronevetsky
Post-Doctoral Researcher
1028 Building 451
Lawrence Livermore National Lab
(925) 424-5756
bronevetsky1@xxxxxxxx