Thanks Dave; we'll finish this up by Monday so that we can get the PDF out in time for a formal reading. Have a great vacation! On Mar 13, 2011, at 1:19 AM, Solt, David George wrote:

I am on vacation this week, so I need to finish up my involvement as I can't say for sure if I will be on e-mail or not during the week.

I checked in the changes I made here:

https://svn.mpi-forum.org/svn/mpi-forum-docs/trunk/working-groups/mpi-3/bw-c...

I uploaded new versions of the pdf's to both tickets with the changes we discussed on Friday. For the issue we are discussing here, I added

"and any value that may be stored in an MPI_Aint type."

but did not add the rationale.

Thanks, Dave

-----Original Message----- From: mpi3-bwcompat-bounces_at_[hidden] [mailto:mpi3-bwcompat-bounces_at_[hidden]] On Behalf Of Rajeev Thakur Sent: Friday, March 11, 2011 11:21 PM To: MPI-3 backwards compatability WG Subject: Re: [Mpi3-bwcompat] MPI Backward Compatibility Working Group

Could we say that MPI_Count should be the larger of MPI_Aint and MPI_Offset? (Anything bigger than that is not really useful.) That might help the I/O problem better.

Rajeev

On Mar 11, 2011, at 11:07 PM, Fab Tillier wrote:

...

Hi Rajeev,

A data buffer can't be larger than MPI_Aint in memory, but an MPI Datatype can be larger than what can fit in memory, and thus larger than MPI_Aint. MPI_Count allows such large datatypes to be represented and used in MPI, even if they can't be held in memory all at once.

This proposal is intended to (minimally) solve the I/O problem, not just large network transfers.

Does that make sense? -Fab

-----Original Message----- From: mpi3-bwcompat-bounces_at_[hidden] [mailto:mpi3-bwcompat-bounces_at_[hidden]] On Behalf Of Rajeev Thakur Sent: Friday, March 11, 2011 8:06 PM To: MPI-3 backwards compatability WG Subject: Re: [Mpi3-bwcompat] MPI Backward Compatibility Working Group

What was the motivation for the new MPI_Type_get_extent_x and MPI_Type_get_true_extent_x functions?

If we say MPI_Count should be at least as large as MPI_Aint, why can't we just use MPI_Aint instead? The data buffer can't be larger than Aint size. I know that for I/O MPI_Offset can be larger than Aint, but this proposal does not solve the I/O problem as far as I know.

https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/265

Rajeev

On Mar 11, 2011, at 5:06 PM, Solt, David George wrote:

...

During our meeting today we decided that MPI_Count should be at least as large as an MPI_Aint. We already had the restriction that it had to be as large as a C/Fortran integer. We want both restrictions (they cannot be combined because there is no guarantee that MPI_Aint > integer).

I'll throw this out as a starting point for discussion:

2.5.8 Last sentence change to:

The size of the MPI_Count type is determined by the MPI implementation with the restriction that it must be minimally capable of encoding a C int and Fortran INTEGER and any value that may be stored in an MPI_Aint type.

Rational thingy:

MPI_Count is used to communicate both the number of elements in a datatype and the bounds of a datatype. The number of elements in a datatype is specified at creation time using a C int or Fortran INTEGER. The bounds may be specified using an MPI_Aint.

So, I was especially brief here. I did not want to get into the "new" routines vs. "old routines", but if you attempt to go into more depth than what I said, you will inevitably end up going down that path. I can think of a thousand ways not to say it, but its hard to come up with a good way. Dave

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