[Mpi3-bwcompat] MPI Backward Compatibility Working Group

[Solt, David George]

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-compat

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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