Good point. At face value, this seems to suggest that we should have "extended" constructors available on a level with the traditional ones, thus favoring the original name-shifted proposal. If I think about the library internals in this case, however, this addition will effectively push all of the library extent calculations to 64-bit (or more, see below).
 
Another thing is that if we multiply to long values, the result may potentially overflow a long. So, for a library that allows long counts and long datatype extents, the internals of the library will have to be long long. long long (128 bit) arithmetic may be rather expensive on some CPUs. So, the 64-bit interface should probably be optional.


From: [email protected] [mailto:[email protected]] On Behalf Of Richard Treumann
Sent: Wednesday, September 03, 2008 7:24 PM
To: MPI 2.2
Subject: Re: [Mpi-22] New proposal: Support for large message counts

MPI_Aint has the right number of bits to hold an address. For operations that are address space oriented, count can be the same size as an MPI_Aint

MPI_Offset has the right number of bits to deal with the range in a file. For operations that are file oriented, arguments like count should be an MPI_Offset

A problem is that MPI_Datatype constructors are intended to apply to both and it is common for a 32 bit address space to operate on files with 64 bit offsets.

What type should "count" on the new "long" MPI_Datatype constructors be in this case? The proposal says MPI_Aint but that is awkward for datatypes as fileviews.


Dick Treumann - MPI Team
IBM Systems & Technology Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846 Fax (845) 433-8363


[email protected] wrote on 09/03/2008 12:38:35 PM:

> [image removed]

>
> Re: [Mpi-22] New proposal: Support for large message counts

>
> Supalov, Alexander

>
> to:

>
> MPI 2.2

>
> 09/03/2008 12:48 PM

>
> Sent by:

>
> [email protected]

>
> Please respond to "MPI 2.2"

>
> Thanks. We may even do without changing the MPI routine names I think.
> Let's consider this:
>
> 1) #define MPI_Count int will yield the current MPI interface.
> 2) typedef int MPI_Count will yield the new 32-bit interface, still
> backward binary compatible with 1).
> 3) typedef long MPI_Count will yield new 64-bit interface.
> 4) typedef long long MPI_Count will safely bring us into XXII century
> (or earlier).
>
> Old applications may be rebuilt using 1) without any changes,
> dynamically linked against MPI library built using 2), and will have to
> be rebuilt to use MPI library built using 3) or 4).
>
> New applications will use library with the MPI_Count definitions, and,
> properly rebuilt, will work in either 32-, 64-, or 128-bit mode, using
> MPI libraries built using MPI bindings 2), 3), or 4), respectively.
>
> By the way, should MPI_Count really be signed?
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Narasimhan,
> Kannan
> Sent: Wednesday, September 03, 2008 5:55 PM
> To: MPI 2.2
> Subject: Re: [Mpi-22] New proposal: Support for large message counts
>
> We can certainly consider this option, since it abstracts along the same
> lines as MPI_Offset.
>
> Thanx!
> Kannan
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Supalov,
> Alexander
> Sent: Wednesday, September 03, 2008 10:19 AM
> To: MPI 2.2
> Subject: Re: [Mpi-22] New proposal: Support for large message counts
>
> Dear Kannan,
>
> Thanks. Why don't we define MPI_Count datatype instead, and make that
> grow if necessary?
>
> Best regards.
>
> Alexander
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Narasimhan,
> Kannan
> Sent: Friday, August 29, 2008 6:15 PM
> To: [email protected]
> Subject: [Mpi-22] New proposal: Support for large message counts
>
> I have submitted a new 2.2 proposal to addresses the need for large
> message counts (i.e. counts greater than the size of 32-bit integer) for
> MPI calls that communicate messages.
>
> Please refer to
> https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/mpi22/LargeMsgCounts
> for details.
>
> Comments and suggestions are welcome.
>
> Thanx!
> Kannan
>
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