[mpich-discuss] determinism in collectives

[Nichols A. Romero]

What about rectangular communicators? Presumably MPI_SUM is optimized even for the MPI_DOUBLE_COMPLEX on a rectangular communicator on BG/Q.

----- Original Message -----
> From: "Jeff Hammond" <jhammond at alcf.anl.gov>
> To: "Pavan Balaji" <balaji at mcs.anl.gov>
> Cc: discuss at mpich.org
> Sent: Monday, November 12, 2012 9:47:29 PM
> Subject: Re: [mpich-discuss] determinism in collectives
> Yes, what I was saying before is that we know that MPI on Blue Gene/Q
> drops into the MPICH2 algorithm for MPI_Reduce on for
> MPI_DOUBLE_COMPLEX with MPI_SUM on irregular communicators and that
> MPIC_Send and MPIC_Recv do not change their behavior on this machine,
> so whatever is true of stock MPICH2 1.4 is true for MPI on Blue
> Gene/Q.
> 
> This confirms what we suspected, which is that BGQ-MPI has
> deterministic reductions in this case because MPICH2 does.
> 
> Jeff
> 
> On Mon, Nov 12, 2012 at 9:43 PM, Pavan Balaji <balaji at mcs.anl.gov>
> wrote:
> >
> > 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
> >>> _______________________________________________
> >>> discuss mailing list discuss at mpich.org
> >>> To manage subscription options or unsubscribe:
> >>> https://lists.mpich.org/mailman/listinfo/discuss
> >>
> >>
> >>
> >
> > --
> > Pavan Balaji
> > http://www.mcs.anl.gov/~balaji
> 
> 
> 
> --
> 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
> _______________________________________________
> discuss mailing list discuss at mpich.org
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-- 
Nichols A. Romero, Ph.D.
Argonne Leadership Computing Facility
Argonne National Laboratory
Building 240 Room 2-127
9700 South Cass Avenue
Argonne, IL 60490
(630) 252-3441