[Mpiwg-large-counts] [Mpi-forum] Announcing/Reconfirming 2nd Vote on Ticket #137 - Enbiggenment (Large Counts)

[Rolf Rabenseifner]

Dear all,

I have trhee concerns and hopefully resolvable through an errata before second vote.

All my references to
https://github.com/mpi-forum/mpi-issues/files/5022345/mpi40-report-ticket137-04Aug2020.pdf

1. Concern:

Sect. 18.2 page 779, lines 32-35 tell:

 The "_l" suffixed MPI procedure has MPI_Count for all count parameters, MPI_Aint for all
 parameters that represent byte displacement in memory, and MPI_Count for all parameters
 that represent byte displacement in files.

MPI_File_seek with MPI_SEEK_CUR moves the file pointer by an offset in bytes in the default fileview is used.

It is also in the _l version defined as MPI_Offset.

In MPI_File_set_view, the "MPI_Offset disp" explicitely defines an "displacement" 
(Sect. 13.3 page 596 line 25).

I expect that this is decided (and in my opinion a good decision), 
but the text in 18.2 should be corrected, for example with an additional 
sentence like

 In MPI_File_... procedures, arguments of type MPI_Offset are not changed to MPI_Count
 although they may contain byte displacements in files.


2. Concern:

It is not described in the 18.2, that "byte displacements in files" is related to
all MPI_File_... and derived datatype procedures.


3. Concern:

I mentioned very early, that the displacement in the derived data type procedures
may be used 
 - for relative displacements used for memeory and files, but never
   in combination with MPI_BOTTOM, or 
 - for absolute displacements in memory in combination with MPI_BOTTOM.

int MPI_Type_create_hindexed(int count, const int array_of_blocklengths[],
const MPI_Aint array_of_displacements[], MPI_Datatype oldtype,
MPI_Datatype *newtype)

can be used for relative and absolute displacements, but only with blocklength in int.

(A) int MPI_Type_create_hindexed_l(MPI_Count count,
const MPI_Count array_of_blocklengths[],
const MPI_Count array_of_displacements[],
MPI_Datatype oldtype, MPI_Datatype *newtype)

can only be used for relative displacements in memory and files,
but not for absolute displ in memory with MPI_BOTTOM.

This means absolute displacements (i.e. with MPI_Aint) together with 
MPI_Count blocklength (B) is missing.

For a few routines a second interface (B) would have been needed.

In my opinion, it is okay to provide A and not B, 
but this should be clearly documented in 18.2.

A simple reason is, that nearly all, what one could do with MPI_BOTTOM,
one can also do with normal buffers, and there, A works.
And A works also for files, but B not.


Summarizing, I expect that the APIs are okay, but 18.2 is missing 
some short explanations of exceptions and decisions.


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: "Anthony Skjellum" <skjellum at gmail.com>
> Sent: Tuesday, August 4, 2020 3:33:53 PM
> Subject: [Mpi-forum] Announcing/Reconfirming 2nd Vote on Ticket #137 - Enbiggenment (Large Counts)

> Hi, this is the two-week vote announcement for Ticket #137, which is already on
> the agenda.
> 
> Issue: [ https://github.com/mpi-forum/mpi-issues/issues/137 |
> https://github.com/mpi-forum/mpi-issues/issues/137 ]
> 
> 
> Pull request: [ https://github.com/mpi-forum/mpi-standard/pull/132 |
> https://github.com/mpi-forum/mpi-standard/pull/132 ]
> 
> PDF: [
> https://github.com/mpi-forum/mpi-issues/files/5022345/mpi40-report-ticket137-04Aug2020.pdf
> |
> https://github.com/mpi-forum/mpi-issues/files/5022345/mpi40-report-ticket137-04Aug2020.pdf
> ]
> One outstanding issue is being discussed, and there may be no-no vote proposed
> also, tbd.
> 
> Thanks,
> Tony and Puri on behalf of the Large Counts WG.
> 
> 
> --
> Anthony Skjellum, PhD
> [ mailto:skjellum at gmail.com | skjellum at gmail.com ]
> Cell: +1-205-807-4968
> 
> 
> 
> 
> 
> 
> _______________________________________________
> mpi-forum mailing list
> mpi-forum at lists.mpi-forum.org
> https://lists.mpi-forum.org/mailman/listinfo/mpi-forum

-- 
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) .