[Mpi3-tools] Questions on the F2008 profiling interface issues

[Schulz, Martin]

Hi Rolf, Craig, and Jeff,

I was in Dresden the last few days (visiting the Vampir group, in
particular Andreas Knuepfer and Tobias Hilbrich who are responsible for
their MPI wrappers) and we sat down to talk about the issues around the
profiling interface in ticket #229.

Here is a quick summary with a few questions that came up:

* With the new Fortran symbol naming variants, there are 6 or 8 or 10
versions for every MPI subroutine. Tools could intercept all versions by
providing own symbols for all versions. Now the problem: Within the
wrapper function a tool needs to call the correct PMPI call which usually
is the same prefix (either '_f08', '_f', '__' etc.) as the MPI call it is
in. A mapping to matching C functions (as most tools do it now) is not
possible due to problems with calling conventions for callback routines.

* This problem is only there for Fortran, since in C we only have one
interface and we are guaranteed that this is always there.

* Would the following solution work? All wrappers for Fortran are written
in Fortran instead of C. For every MPI function, there are 6 or 8 variants
and all of them need to be provided by a tool. This would probably mean
that we have to compile wrappers with all three calling conventions
(mpif.h, use mpi_f and use mpi_f08) and then link them together?

Then within the Fortran wrappers, one could safely call the plain Fortran
name
of the PMPI function. Based on the specification of the standard, the MPI
implementation would then provide a matching Fortran "P" call that the
Fortran compiler then needs to transform into the correct symbol name with
one of the prefixes, the same way it works for the regular "MPI" routines.
Does this sound right or are we missing something? Does this separate
compilation of tool wrappers using all three methods and then linking them
together really work?

* I think you mentioned this before, but I forgot - why is the BINDC
option in Chapter 16 coupled to the SUBARRAYS flag? Why are those not
separate issue?

* As discussed at the forum, if we want to keep our tools in C (which is
probably still the easier and better option), we need to know the symbols
on the "p" side and we need a portable way to figure this out. We talked
about the solution of two groups of routines - one for which we have _f08
symbols for one for which we don't. Rolf, how will you add this to the
standard, in particular how will you form those groups.

* Once we have the groups, is the following correct?
** If the symbol pmpi_foo exists, then pmpi_bar exists for any bar
** If the symbol pmpi_foo_ exists, then pmpi_bar_ exists for any bar
** If the symbol pmpi_foo__ exists, then pmpi_bar__ exists for any bar
** If the symbol PMPI_Foo_f exists, then PMPI_Bar_f exists for any bar
** If the symbol pmpi_foo_f08 exists, then pmpi_bar_f08 exists for any bar
in the group of _f08 routines defined in the standard, but does not exist
for any other bar




** If the symbol pmpi_foo_f08_ exists, then pmpi_bar_f08_ exists for any
bar in the group of _f08 routines defined in the standard, but does not
exist for any other bar
** If the symbol pmpi_foo_f08__ exists, then pmpi_bar_f08__ exists for any
bar in the group of _f08 routines defined in the standard, but does not
exist for any other bar
** If the symbol PMPI_Foo_f08 exists, then PMPI_Bar_f08 exists for any bar
in the group of _f08 routines defined in the standard, but does not exist
for any other bar
Is this correct and complete or am I missing any symbols.

Does this all sound correct? We just wanted to make sure we understand all
the nuances  and have things right before the discussion on Monday.

Thanks!

Martin








-- 
________________________________________________________________________
Martin Schulz, schulzm at llnl.gov, http://people.llnl.gov/schulzm
CASC @ Lawrence Livermore National Laboratory, Livermore, USA