[mpich-discuss] determinism in collectives

Jeff Hammond jhammond at alcf.anl.gov
Mon Nov 12 21:40:48 CST 2012

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.


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
> _______________________________________________
> discuss mailing list     discuss at mpich.org
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/discuss

Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381

More information about the discuss mailing list