> On Jan 23, 2009, at 6:32 AM, Gabriele Fatigati wrote:
>> I've noted that OpenMPI has an asynchronous behaviour in the collective
>> The processors, doesn't wait that other procs arrives in the call.
> That is correct.
>> This behaviour sometimes can cause some problems with a lot of
>> processors in the jobs.
> Can you describe what exactly you mean? The MPI spec specifically allows
> this behavior; OMPI made specific design choices and optimizations to
> support this behavior. FWIW, I'd be pretty surprised if any optimized MPI
> implementation defaults to fully synchronous collective operations.
>> Is there an OpenMPI parameter to lock all process in the collective
>> call until is finished? Otherwise i have to insert many MPI_Barrier
>> in my code and it is very tedious and strange..
> As you have notes, MPI_Barrier is the *only* collective operation that MPI
> guarantees to have any synchronization properties (and it's a fairly weak
> guarantee at that; no process will exit the barrier until every process has
> entered the barrier -- but there's no guarantee that all processes leave the
> barrier at the same time).
> Why do you need your processes to exit collective operations at the same
> Jeff Squyres
> Cisco Systems
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