[MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind
Rolf Rabenseifner
rabenseifner at hlrs.de
Thu Mar 21 02:44:06 CDT 2013
Thank you for the answers. Four comments:
1. About the linker names and intenal call sequence:
>> I think that Bill's proposal kills the Fortran Profiling Interface.
>> If the user defines a
>> subroutine MPI_Test (....)
>> do something
>> call PMPI _Test()
>> do something
>> end subroutine MPI_Test
Yes, this is true. Having these two implementation options
A. Internal real MPI C calls with
A1. standardized Fortran linker names, or with
A2. non-standardized Fortran names, i.e. within a Fortran module.
B. Standardized Fortran linker names.
would kill the upper Fortran example as soon as an implementation
chooses A2.
Bill, do you have an idea how to solve the A2 problem.
Is it still possible to provide the standardized names
when you somehow inline the wrappers?
Then, we would have only A1 which allows that a pure PMPI
Fortran user can freely choose to intercept the Fortran
or the C interface.
2. About MPI_Send_desc:
Yes, Bill, you are absolutely right.
I thought that the MPI_Isend_desc internally calls MPI_Isend,
but this would be an implementation that internally
copies the non-contiguous Fortran application buffer
into a contiguous scratch buffer and then calls MPI_Isend
(the scratch buffer is released latest in MPI_Wait or MPI_Test).
Optimized solutions would do flattening on the fly
of the combination of the description of the Fortran buffer
combined with the description in the datatype handle,
and this double-flattening within the MPI_Isend_desc.
Therefore special naming for option A must be defined.
This is only for the MPI routine groups MPI_SEND
and MPI_ISEND (see MPI-3.0, page 607 and ticket #364)
3. Routine groups:
All what we do should be done per routine group,
i.e., mpi.h tells by macros how it is done within
the specific routine groups.
4. My apologies to Hubert.
The list should have been
> >> I need at least answers for
> >> - mpich (Bill Long),
> >> - OpenMPI (Jeff or Craig),
- NEC MPI (Hubert),
- other, if there are other independent
mpi_f08 implementations,
> >> - some tools people.
Best regards
Rolf
----- Original Message -----
> From: "Bill Long" <longb at cray.com>
> To: "Jeff Squyres (jsquyres)" <jsquyres at cisco.com>
> Cc: "Martin Schulz" <schulzm at llnl.gov>, "MPI-3 Fortran working group" <mpi3-fortran at lists.mpi-forum.org>
> Sent: Wednesday, March 20, 2013 9:40:08 PM
> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind
> My impression is that Rolf's proposal was to offer two options:
>
> a) no bind(c) on the Fortran wrappers, no requirements on the Fortran
> external names, but the wrappers are REQUIRED to call the C library
> routines.
>
> b) specific external names are required for the Fortran-called
> routines,
> but they do not have to be wrappers. (Still a bit unclear to me in
> this case where bind(c) might be required).
>
> On 3/20/13 2:58 PM, Jeff Squyres (jsquyres) wrote:
> > Not only that, I think that there are some cases where tools *need*
> > to intercept the Fortran call, not the C call. In OMPI, for example,
> > we have a few corner cases where the Fortran MPI subroutine does
> > *not* call the corresponding C MPI API function. Instead, it calls a
> > back-end OMPI routine.
> >
>
> True for implementations using option (b), but not for the (a) case.
>
> > One obvious case that jumps to mind is anything involving a
> > callback.
>
> Looking at the callback examples on page 268, I have some questions:
>
> 1) The BIND(C) and an argument of type LOGICAL are likely
> incompatible,
> so either the BIND(C) or the LOGICAL needs to go.
>
> 2) The external names for the C and Fortran versions are different. I
> assume this does not matter assuming that the function that is calling
> these has only an address, and not a name, to call. But how does the
> function know the calling signature for the callback routine with only
> a
> procedure pointer to work with?
>
> If I were writing a code with a callback like this, I would want to
> assume the C prototype even of the code was in Fortran. I assume the
> existence of the separate (and apparently flawed) Fortran interface is
> for legacy code. But there should not be legacy mpi_f08 code. A bit
> confusing.
>
> >
> > If you have integer handles in C, they might be able to get away
> > with not swizzling/de-swizzling the arguments to the callback to the
> > proper language. But this is not always the case.
> >
> >
> >
> > On Mar 20, 2013, at 12:29 PM, Hubert Ritzdorf
> > <Hubert.Ritzdorf at emea.nec.com> wrote:
> >
> >> Hi,
> >>
> >> I think that Bill's proposal kills the Fortran Profiling Interface.
> >>
> >> If the user defines a
> >>
> >> subroutine MPI_Test (....)
> >>
> >> do something
> >>
> >> call PMPI _Test()
> >>
> >> do something
> >>
> >> end subroutine MPI_Test
>
> I was under the impression that users would not directly call PMPI
> routines. Those were for the tools people. Why would a normal user
> want to do something like the above?
>
> >>
> >> then this function will never be executed because the Fortrran
> >> compiler may have already
> >> inlined the MPI_Test subroutine in the original code or the module
> >> version of MPI_Test is used.
>
> In the scope where this routine is called, the Fortran wrapper would
> have to be inaccessible. That would be done by NOT having a USE of the
> module in this scope. The external name of the module procedure would
> be
> mangled to include the name of the module, whereas a stand-alone
> routine like this would have an external name like mpi_test_ . The
> linker would see these as different routines.
>
>
> Cheers,
> Bill
>
>
> >>
> >> Hubert
> >> ________________________________________
> >> From: mpi3-fortran-bounces at lists.mpi-forum.org
> >> [mpi3-fortran-bounces at lists.mpi-forum.org] on behalf of Rolf
> >> Rabenseifner [rabenseifner at hlrs.de]
> >> Sent: Wednesday, March 20, 2013 6:09 PM
> >> To: longb at cray.com; MPI-3 Fortran working group
> >> Cc: Martin Schulz
> >> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008
> >> interface - issue with the LOGICAL kind
> >>
> >> This mail contains a proposal how we can solve the current
> >> Fortran problems and possibly making the tools people also happy.
> >>
> >> I need at least answers for
> >> - mpich (Bill Long),
> >> - OpenMPI (Jeff or Craig),
> >> - some tools people.
> >>
> >> Let me summarize what I've learnt so far for mpi_f08:
> >>
> >> - #364 about LOGICAL correction is a must.
> >> - MPI-3.0 allows BIND(C) and non-BIND(C), with the
> >> new restrictions in #364
> >> - BIND(C) needs TR29113, therefore any implementation now
> >> should use non-BIND(C) for all non-TR29113 compilers.
> >> - Most (or all) try to use the non-BIND(C) interface.
> >> - Best way to do this are thin wrappers in Fortran that
> >> internally call
> >> - the oficial MPI-3.0 C binding
> >> (here, the tools people have a problem because they
> >> expect to wrap the Fortran interface and may therefore
> >> double-wrap), or
> >> - or an internal MPI-3.0 C routine
> >> (which is half-perfect for the tools folk, because
> >> they have to handle the implementation-dependant
> >> Fortran names with underscores).
> >> - And at least Bill wants to include the Fortran MPI
> >> library routines itselves in the mpi_f08 module.
> >> This is in conflict with the current MPI-3.0
> >> linker naming rules.
> >>
> >> Implications and proposal:
> >> - We should rewrite the linker names section MPI-3.0 17.1.5
> >> with following goals:
> >> - Allow additionally to define that the PMPI is provided
> >> only on the MPI C interface and the Fortran MPI routines
> >> internally call the C interface;
> >> again, a macro definition in mpi.h tells whether this
> >> is chosen.
> >> Question: Would this cause a problem when linking a
> >> C or Fortran user application with some own
> >> MPI_Test etc. profiling routines that internally call
> >> PMPI_Test?
> >> - If Fortran profiling is done through the MPI C binding
> >> then there are no rules about the Fortran linker names
> >> needed, and therefore, one may put the thin Fortran
> >> wrappers into a Fortran module.
> >> - We can define BIND(C) for MPI routine groups as a
> >> future option that is currently not used.
> >> This would reduce the current effort for the tools people.
> >> Is there anybody who wants to implement one of the Fortran
> >> routine groups with BIND(C)?
> >>
> >> I would expect, that this is the best to solve the problem
> >> that #364 prohibits BIND(C) for some routines and implementors
> >> want to do the same method for all routines.
> >>
> >> Don't forget that BIND(C) and TR29113 is still important
> >> for implementing these thin wrappers internally.
> >>
> >> Without using BIND(C) on the official mpi_f08 and mpi module
> >> interface, some features of TR29113 are not used:
> >> - the extension for interoperabple CHARACTER(LEN=*),
> >> - the extension for OPTIONAL dummy arguments.
> >>
> >> Other TR29113 features are heavily used:
> >> - The DIMENSION(..), TYPE(*) is needed for some internal
> >> C-written MPI_Isend_desc.
> >> - The ASYNCHRONOUS usage for communication buffers.
> >>
> >> Should we go in this direction?
> >>
> >> Best regards
> >> Rolf
> >>
> >>
> >> ----- Original Message -----
> >>> From: "Bill Long" <longb at cray.com>
> >>> To: "Jeff Squyres (jsquyres)" <jsquyres at cisco.com>
> >>> Cc: "Martin Schulz" <schulzm at llnl.gov>, "MPI-3 Fortran working
> >>> group" <mpi3-fortran at lists.mpi-forum.org>
> >>> Sent: Wednesday, March 20, 2013 4:01:52 PM
> >>> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008
> >>> interface - issue with the LOGICAL kind
> >>> On 3/20/13 8:26 AM, Jeff Squyres (jsquyres) wrote:
> >>>> On Mar 20, 2013, at 6:25 AM, Bill Long <longb at cray.com> wrote:
> >>>>
> >>>>> interface !--> MPI_Test
> >>>>>
> >>>>> ! int MPI_Test(MPI_Request *request, int *flag, MPI_Status
> >>>>> *status);
> >>>>>
> >>>>> Function MPI_Test_C( request, flag, status) &
> >>>>> BIND(C, name="MPI_Test") RESULT (res)
> >>>>> import :: C_request, c_int, MPI_Status_C
> >>>>> integer(C_request) :: request
> >>>>
> >>>> This is not correct. You cannot assume that MPI handles are
> >>>> integers
> >>>> (they're pointers in Open MPI).
> >>>
> >>>
> >>> This is correct for mpich. OpenMPI would evidently have a
> >>> different
> >>> version. But the concept is still the same - make a correct
> >>> interface
> >>> to the C library routine, however it is defined by the
> >>> implementation,
> >>> and then call that from a thin Fortran wrapper that takes care of
> >>> the
> >>> issues related to LOGICAL, the use of default INTEGER, and
> >>> OPTIONAL
> >>> arguments.
> >>>
> >>> Cheers,
> >>> Bill
> >>>
> >>>
> >>>>
> >>>
> >>> --
> >>> Bill Long longb at cray.com
> >>> Fortran Technical Support & voice: 651-605-9024
> >>> Bioinformatics Software Development fax: 651-605-9142
> >>> Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101
> >>>
> >>>
> >>> _______________________________________________
> >>> mpi3-fortran mailing list
> >>> mpi3-fortran at lists.mpi-forum.org
> >>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
> >>
> >> --
> >> Dr. Rolf Rabenseifner . . . . . . . . . .. email
> >> rabenseifner at hlrs.de
> >> High Performance Computing Center (HLRS) . phone
> >> ++49(0)711/685-65530
> >> University of Stuttgart . . . . . . . . .. fax ++49(0)711 /
> >> 685-65832
> >> Head of Dpmt Parallel Computing . . .
> >> www.hlrs.de/people/rabenseifner
> >> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room
> >> 1.307)
> >> _______________________________________________
> >> mpi3-fortran mailing list
> >> mpi3-fortran at lists.mpi-forum.org
> >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
> >>
> >>
> >> Click
> >> https://www.mailcontrol.com/sr/oUBxarVXlArGX2PQPOmvUrwgXREt4LZXdolWasoQmWDbX5aSB7TlS9if4+7oDyxaXeCWFTId+Sn5pl0FDW8fzw==
> >> to report this email as spam.
> >>
> >> _______________________________________________
> >> mpi3-fortran mailing list
> >> mpi3-fortran at lists.mpi-forum.org
> >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
> >
> >
>
> --
> Bill Long longb at cray.com
> Fortran Technical Support & voice: 651-605-9024
> Bioinformatics Software Development fax: 651-605-9142
> Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101
>
>
> _______________________________________________
> mpi3-fortran mailing list
> mpi3-fortran at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
--
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
More information about the mpiwg-fortran
mailing list