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

[Narasimhan, Kannan]

Alexander,

Thanx for the suggestion.

1. Maybe I'm missing something here, but without name change, we break backward compatibility with "old" binaries coded to the existing APIs with 32-bit counts, and the new MPI 2.2 compatible MPI shared library that supports 64-bit counts --- without a re-build/relink step. Or are you proposing that implementations have multiple libraries, one that supports 32 bit counts, one that supports 64 bit counts, etc.? With a single library, (1) and (2) addresses backward compatibility, but maintains status-quo on support for large message counts, and (3) and (4) requires rebuild. However, having different names will take care of this.

2. If needed, we can explore normalization to a single API that supports MPI_Count in the MPI 3.0 time frame, since MPI 3.0 is open changes that can break backward compatibility.

3. I cannot think of any use cases for a "signed" count, but I'll let others chime in here.

4. I agree that new applications will have no issues with your approach.

Thanx!
Kannan

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander
Sent: Wednesday, September 03, 2008 11:39 AM
To: MPI 2.2
Subject: Re: [Mpi-22] New proposal: Support for large message counts

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: mpi-22-bounces_at_[hidden]
[mailto:mpi-22-bounces_at_[hidden]] 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: mpi-22-bounces_at_[hidden]
[mailto:mpi-22-bounces_at_[hidden]] 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: mpi-22-bounces_at_[hidden]
[mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Narasimhan, Kannan
Sent: Friday, August 29, 2008 6:15 PM
To: mpi-22_at_[hidden]
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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