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Subject: Re: [OMPI users] Algorithms used in MPI_BCast
From: Pavel Mezentsev (pavel.mezentsev_at_[hidden])
Date: 2012-09-24 09:09:04


Hello,

Are you making these rules manually or in some automated way?

Regards, Pavel Mezentsev.

2012/9/21 Iliev, Hristo <iliev_at_[hidden]>

> Hi,
>
> Open MPI uses several different algorithms depending on which module from
> the "coll" framework is selected to perform the logic of the broadcast
> operation. The "tuned" module which usually gets selected on cluster
> installations uses a heuristic rule, based on the message size and the size
> of the communicator, to choose between building a pipeline, binomial tree
> or
> split binary tree. There are also other algorithms that go unused by the
> default rule logic, but you can force them with MCA parameters if you'd
> like.
>
> The default rules might not be optimal for your hardware. You can
> reevaluate
> each algorithm and create a rule file that you can then give to Open MPI.
> That's what I'm doing now on our cluster.
>
> Kind regards,
> Hristo
> --
> Hristo Iliev, Ph.D. -- High Performance Computing
> RWTH Aachen University, Center for Computing and Communication
> Rechen- und Kommunikationszentrum der RWTH Aachen
> Seffenter Weg 23, D 52074 Aachen (Germany)
> Tel: +49 241 80 24367 -- Fax/UMS: +49 241 80 624367
>
>
> > -----Original Message-----
> > From: users-bounces_at_[hidden] [mailto:users-bounces_at_[hidden]]
> > On Behalf Of Mohammed El Mehdi DIOURI
> > Sent: Friday, September 21, 2012 2:13 AM
> > To: users_at_[hidden]
> > Cc: Mohammed El Mehdi DIOURI
> > Subject: [OMPI users] Algorithms used in MPI_BCast
> >
> > Hi,
> >
> > I would like to know what are the algorithms used in MPI_BCast() in the
> > OpenMPI implementation.
> >
> > For example, in MPICH2, depending on the number of processes and the size
> > of data to broadcast, the broadcasting algorithm used can be different :
> a
> > binomial tree if the message is short or MPI_Scatter followed by
> > MPI_AllGather if the message to broadcast is long.
> >
> > Is it the same for OpenMPI ?
> > It doesn't seem to be the case since the broadcasting time is different
> when I
> > use OpenMPI or MPICH2.
> >
> > Thanks for your help,
> >
> > Mehdi.
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
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