[Mpi-forum] Big Fortran hole in MPI-4.0 Embiggening

Mon Jan 11 06:26:00 CST 2021

Dear Jeff and all,

> I think their users would be very unhappy.

Yes, users can be unhappy and compute centers may definitely recommend 
an other MPI library - at least for any software development.

I want to remember that MPI-3.1 requires for the mpi module:

"Provide explicit interfaces according to the Fortran routine interface specications.
This module therefore guarantees compile-time argument checking and allows positional
and keyword-based argument lists. If an implementation is paired with a
compiler that either does not support TYPE(*), DIMENSION(..) from TS 29113, or
is otherwise unable to ignore the types of choice buffers, then the implementation must
provide explicit interfaces only for MPI routines with no choice buer arguments. See
Section 17.1.6 for more details."

Although there are no more such compilers that do not provide one of the two methods,
there are more than 5 years after MPI-3.1 still MPI libraries that do not
provide keyword-based argument lists with the mpi module.
And those libraries provide such support for the mpi_f08 module.
This means, they prove that they are not MPI-3.1 compliant :-)

Sometimes implementors ignore the goals and the wording of the MPI standard. 

And there is also no request that users want to have a less-quality
mpi module definition.

Best regards
Rolf

----- Original Message -----
> From: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
> To: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
> Cc: "Jeff Squyres" <jsquyres at cisco.com>
> Sent: Sunday, January 10, 2021 5:09:55 PM
> Subject: Re: [Mpi-forum] Big Fortran hole in MPI-4.0 Embiggening

> I can't imagine a vendor would:
> 
> - support mpi_f08
> - then stop supporting mpi_f08 just so that they can get an "MPI-4.0" release
> out
> - then support mpi_f08 again
> 
> I think their users would be very unhappy.
> 
> 
> 
> 
> 
> On Jan 10, 2021, at 10:55 AM, William Gropp via mpi-forum < [
> mailto:mpi-forum at lists.mpi-forum.org | mpi-forum at lists.mpi-forum.org ] > wrote:
> 
> I agree with Dan that this is a big change from the RCM. Further, the approach
> in MPI has always been to encourage the users to make it clear to the vendors
> what is acceptable in implementations, especially implementation schedules.
> Nothing in the standard prohibits implementors from continuing to provide MPI
> 3.x implementations while they work to provide a full MPI 4.0 implementation.
> The MPI forum has no enforcement power on the implementors, and I believe this
> text is unnecessary and will not provide the guarantee that Rolf wants.
> Further, frankly once the C embiggened interface is implemented, creating the
> mpi_f08 version is relatively straightforward.
> 
> Bill
> 
> William Gropp
> Director, NCSA
> Thomas M. Siebel Chair in Computer Science
> University of Illinois Urbana-Champaign
> IEEE-CS President-Elect
> 
> 
> 
> 
> 
> 
> On Jan 10, 2021, at 7:44 AM, HOLMES Daniel via mpi-forum < [
> mailto:mpi-forum at lists.mpi-forum.org | mpi-forum at lists.mpi-forum.org ] > wrote:
> 
> Hi Rolf,
> 
> This is a (somewhat contrived, arguably) reason for taking another tiny step
> towards removing the “mpif.h” method of Fortran support and pushing users and
> implementations towards preferring the Fortran 2008 interface, which is a
> direction of travel that I fully support.
> 
> I think this might be seen as quite a big change for implementers, especially if
> it were to occur between the RCM and FRM.
> 
> Cheers,
> Dan.
> —
> Dr Daniel Holmes PhD
> Architect (HPC Research)
> [ mailto:d.holmes at epcc.ed.ac.uk | d.holmes at epcc.ed.ac.uk ]
> Phone: +44 (0) 131 651 3465
> Mobile: +44 (0) 7940 524 088
> Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT
> —
> The University of Edinburgh is a charitable body, registered in Scotland, with
> registration number SC005336.
> —
> 
> 
> 
> 
> On 10 Jan 2021, at 12:22, Rolf Rabenseifner via mpi-forum < [
> mailto:mpi-forum at lists.mpi-forum.org | mpi-forum at lists.mpi-forum.org ] > wrote:
> 
> This email was sent to you by someone outside the University.
> You should only click on links or attachments if you are certain that the email
> is genuine and the content is safe.
> 
> Dear MPI-Forum members,
> 
> MPI-3.1 and MPI-4.0 includes the following rule on top of the 2nd page
> of the Language Binding chapter:
> 
>| MPI implementations providing a Fortran interface must provide
>| one or both of the following:
>| - The USE mpi_f08 Fortran support method.
>| - The USE mpi and INCLUDE 'mpif.h' Fortran support methods.
> 
> The embiggening was included only in the C and mpi_f08 bindings.
> 
> Most implementors nowadays provide all three MPI Fortran support methods,
> i.e., the mpi_f08 and the mpi module and mpif.h.
> 
> For all MPI-3.1 libraries that provide all three MPI Fortran support methods,
> the most easiest and fastest way to provide MPI-4.0 for C and Fortran is,
> - to implement the embiggening for C,
> - and to remove the mpi_f08 module,
> - and maybe months or years later, to provide mpi_f08 again, now embiggened.
> 
> This implementation path (by removing mpi_f08 from MPI-3.1 and to name
> it MPI-4.0 without Fortran embiggening) was of course never intended,
> when we decided to require the embiggened routines only for mpi_f08.
> The goal was
> - to not require additional work from the implementors for the old mpi module
> - convince the users that it is a good idea to make a transition
> to mpi_f08.
> 
> The most simplest way to resolve this problem would be to require
> mpi_f08 for MPI-4.0, i.e., to change the text to
> 
>| MPI implementations providing a Fortran interface
>| - must provide the USE mpi_f08 Fortran support method,
>| - and additionally may provide both,
>| the USE mpi and INCLUDE 'mpif.h' Fortran support methods.
> 
> What is your opinion?
> 
> I expect that we should discuss this next Wednesday at our MPI Forum telcon.
> 
> Best regards
> Rolf
> 
> --
> Dr. Rolf Rabenseifner . . . . . . . . . .. [ mailto:rabenseifner at hlrs.de | email
> rabenseifner at hlrs.de ] .
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-- 
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) .