[Mpi3-rma] FW: MPI_Accumulate

[Pavan Balaji]

Put is not byte wise atomic.  It is not atomic at all.  Only the accumulate-style operations are predefined datatype granularity atomic.

--
Pavan Balaji
http://www.mcs.anl.gov/~balaji

On Oct 2, 2012, at 11:48 AM, Jeff Hammond <jhammond at alcf.anl.gov> wrote:

> My understanding has always been that MPI_Accumulate was and is atomic
> at granularity of the underlying built-in datatype, as opposed to
> byte-wise atomic like MPI_Put.  This is the whole reason that
> MPI_Accumulate w/ MPI_REPLACE exists.  Without the additional
> atomicity guarantee, that feature would be pointless.
> 
> Jeff
> 
> On Tue, Oct 2, 2012 at 11:38 AM, Richard Graham <richardg at mellanox.com> wrote:
>> resending
>> 
>> 
>> 
>> From: Richard Graham
>> Sent: Tuesday, October 02, 2012 12:22 PM
>> To: MPI 3.0 Remote Memory Access working group
>> (mpi3-rma at lists.mpi-forum.org)
>> Subject: MPI_Accumulate
>> 
>> 
>> 
>> What are the requirements placed on MPI_Accumulate if more than one mpi
>> process tries to update the same location ?  Does MPI provide any
>> consistency promises, or is it up to the application to guarantee these ?  I
>> see that the get accumulate routines are defined to be atomic, but don’t see
>> the same requirement for accumulate.
>> 
>> 
>> 
>> Thanks,
>> 
>> Rich
>> 
>> 
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> 
> 
> 
> -- 
> Jeff Hammond
> Argonne Leadership Computing Facility
> University of Chicago Computation Institute
> jhammond at alcf.anl.gov / (630) 252-5381
> http://www.linkedin.com/in/jeffhammond
> https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond
> 
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