Newsgroups: comp.parallel.mpi
From: rbarrett@ranger.lanl.gov (Richard Barrett)
Subject: Re: reductions deterministic?
Organization: Los Alamos National Laboratory
Date: 18 Mar 1996 17:59:59 GMT
Message-ID: <4ik8av$g9k@newshost.lanl.gov>

Bill,

Thanks for the information. However, that's quite an important caveat: getting the
same answer with a varying number of processors is worth the loss of performance
for some users. If fact if they don't get it, they will claim our code is "broken" 
and won't use it. Would it be possible to provide a fully deterministic version 
option?

Richard

In article <8269889271688@godzilla.mcs.anl.gov>, gropp@godzilla.mcs.anl.gov (William Gropp) writes:
|> In article <4ics0k$3e8@newshost.lanl.gov>,
|> Richard Barrett <rbarrett@ranger.lanl.gov> wrote:
|> >In its "advice to implementors" it is "strongly recommended" that MPI reductions
|> >be deterministic. Can anyone please tell me if this recommendation has
|> >been followed by:
|> >
|> >- MPICH (including MPP versions) 
|> 
|> Yes.  But note that deterministic applies to the exact same situation (number
|> of processors, order of members in group).  It says nothing about differing
|> numbers of processors (which some would also like, but which seriously 
|> impacts performance).
|> 
|> Bill

