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

Thu Sep 4 03:58:11 CDT 2008

Hi,

Yes, I was looking into maintaining one library source code with the
ability to build several versions out of it. Since 1) and 2) will be
essentially ABI compatible, one can ship one version of the 32-bit
dynamic library to cover both cases. The 64-bit library will be
different, and this is I think what customers want anyway - they don't
seem to want mixing 32- and 64-bit calls in one application.

Best regards.

Alexander 

-----Original Message-----
From: mpi-22-bounces_at_[hidden]
[mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Narasimhan,
Kannan
Sent: Wednesday, September 03, 2008 7:32 PM
To: MPI 2.2
Subject: Re: [Mpi-22] New proposal: Support for large message counts

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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