[mpich-discuss] determinism in collectives

[Pavan Balaji]

The default machine-independent implementation of MPICH is
deterministic.  However, each device can (and most times does) implement
its own version of MPI_Reduce.  We have no control on them.

 -- Pavan

On 11/12/2012 09:40 PM US Central Time, Jeff Hammond wrote:
> We are primarily interested in MPICH2, as the motivation for this
> question relates to a particular supercomputer that uses MPICH2 and,
> in particular, the MPICH2 implementation of MPI_Reduce for
> (comm,type,op) of interest to us.
> 
> Jeff
> 
> On Mon, Nov 12, 2012 at 9:35 PM, Pavan Balaji <balaji at mcs.anl.gov> wrote:
>>
>> The MPI standard does not guarantee this.  For example, an
>> implementation could use topology-aware reductions or an MPI_ANY_SOURCE
>> while waiting for messages from peers making the order in which the
>> reduction operations are applied different for each run.
>>
>>  -- Pavan
>>
>> On 11/12/2012 09:00 PM US Central Time, Nichols A. Romero wrote:
>>> Hi,
>>>
>>> I apologize if this has been asked a trillion times, if its documented somewhere just point it out to me online.
>>>
>>> Are collective operations, such as sums, using MPI_Reduce deterministic? In other words, if I run MPI_Reduce N times on P tasks, will the sums always occur in the same order. Thus it would be reproducible to the expected precision.
>>>
>>
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
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> 
> 
> 

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