[Mpiwg-large-counts] A perfect trick in C with similar API as with Fortran overloading - instead of the many new _l functions in C

[Tony Skjellum]

Rolf, the group has labored over each area... 1 sided has had the least attention so far... All of MPI is to be made 64 bit clean not parts.

Partial answer to your earliest question in the note: Changing the meaning of existing APIs was disallowed some time ago.  Certainly, for in arguments of count , replacing int with MPI_Count is a partial solution.  But it changes the APIs ... 

In C, a program written for the assumption of big count and compiled accidentally with an MPI-3 compliant MPI will silently build and fail at runtime ... rounding of integers ... and changing the AbI violates the ABI for tools and such  — two  possible reasons why not chosen ... but we will have to go refresh on all the reasons .  

I am sure you will get extensive feedback on these questions from the whole group ? :-) 

Tony 

Anthony Skjellum, PhD
205-807-4968


> On Oct 20, 2019, at 2:25 PM, Rolf Rabenseifner via mpiwg-large-counts <mpiwg-large-counts at lists.mpi-forum.org> wrote:
> 
> Dear all,
> 
> a participant in my latest course asked me, whether we not 
> substituting in by MPI_Count in all "int xxxxx" input arguments.
> The compiler automatically would cast to MPI_Count which may be a fast
> instruction. Then we need the new _x or _l functions only for those
> rare functions with MPI_Count as output or array argument.
> 
> Was this ever discussed?
> 
> Second question:
> Does the large Count roup plan, only to use MPI_Count for data, 
> i.e., only in communication, I/O, and derived type routines?
> 
> Is it correct, that we keep the number of 
> - request handles in request arrays,
> - ranks an size in/of communicator and group handles,
> will stay int?
> 
> How do we handle disp in 1-sided communication?
> 
> With this approach, it seems that explicit MPI_Count versions of
> a subroutine is needed only for
> MPI_[I][NEIGHBOR_]{ALLTOALL|ALLGATHER}{V|W} 
> MPI_[I]{GATHER|SCATTER}V
> MPI_[I]REDUCE_SCATTER
>  (18 routines)
> MPI_WIN_SHARED_QUERY --> *disp
>  (1 Routine)
> MPI_[UN]PACK
> MPI_PACK_SIZE _x/_l version should have MPI_Aint (same as for MPI_...PACK..._external)  
>  (3 routines)
> MPI_GET_COUNT
> MPI_GET_ELEMENTS (has already an _X version)
> MPI_TYPE_SIZE (has already an _X version)
> 
> Which solution exists for MPI_CONVERSION_FN_NULL?
> 
> All other 100 routines with "int count" and "int size" seems
> to be solved with directly changing it into "MPI_Count count" and "MPI_Count size". 
> 
> Best regards
> Rolf
> 
> ----- Original Message -----
>> From: "mpiwg-large-counts" <mpiwg-large-counts at lists.mpi-forum.org>
>> To: "mpiwg-large-counts" <mpiwg-large-counts at lists.mpi-forum.org>
>> Cc: "Jeff Squyres" <jsquyres at cisco.com>
>> Sent: Saturday, October 19, 2019 10:26:23 PM
>> Subject: [Mpiwg-large-counts] Pythonizing instructions
> 
>> As discussed in our last meeting, I've written a first take at instructions for
>> Chapter Authors for how to write Pythonized functions.
>> 
>> These instructions are not yet intended for a wide audience -- they are intended
>> solely for the working group.  Let's iterate on them here in the WG and get
>> them to a good enough state before sharing them widely:
>> 
>>   https://github.com/mpiwg-large-count/large-count-issues/wiki/pythonizing
>> 
>> Puri/Tony/Dan: please try to use these instructions to Pythonize a few bindings.
>> The PR for the Pythonization is
>> https://github.com/mpiwg-large-count/mpi-standard/pull/2.  All even-numbered
>> chapters are done, and a small number of odd-numbered chapters.  Grep for
>> `funcdef` in chapter *.tex files to find a chapter that hasn't been Pythonized
>> yet (funcdef is the LaTeX macro for hard-coded LaTeX macros).
>> 
>> Send your feedback here and/or we'll discuss on Wednesday.
>> 
>> --
>> Jeff Squyres
>> jsquyres at cisco.com
>> 
>> _______________________________________________
>> mpiwg-large-counts mailing list
>> mpiwg-large-counts at lists.mpi-forum.org
>> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-large-counts
> 
> -- 
> 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) .
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