[Mpi3-rma] FW: MPI_Accumulate

[Jeff Hammond]

Okay, sorry, I was assuming that no one makes hardware that is less
than byte-wise atomic.  I suppose an implementation could do as I
suggested at some point and write the bit representation of "POOP" to
memory for conflicting writes, but this seems like it would be slower
than just doing conflicting writes and letting the memory controller
figure it out.

Jeff

On Tue, Oct 2, 2012 at 1:22 PM, Pavan Balaji <balaji at mcs.anl.gov> wrote:
>
> 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
>>>
>>>
>>> _______________________________________________
>>> mpi3-rma mailing list
>>> mpi3-rma at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>
>>
>>
>> --
>> 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
>>
>> _______________________________________________
>> mpi3-rma mailing list
>> mpi3-rma at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>
> _______________________________________________
> mpi3-rma mailing list
> mpi3-rma at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma



-- 
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