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Subject: Re: [OMPI users] Question about Asynchronous collectives
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2010-09-23 10:00:58


Mm,

to be sure, if i have one processor who does:

MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast
MPI_IBcast(MPI_COMM_WORLD, request_2) // second Bcast

it means that i can't have another process who does the follow:

MPI_IBcast(MPI_COMM_WORLD, request_2) // firt Bcast for another process
MPI_IBcast(MPI_COMM_WORLD, request_1) // second Bcast for another process

Because first Bcast of second process matches with first Bcast of first
process, and it's wrong.

Is it right?

2010/9/23 Jeff Squyres <jsquyres_at_[hidden]>

> On Sep 23, 2010, at 6:28 AM, Gabriele Fatigati wrote:
>
> > i'm studing the interfaces of new collective routines in next MPI-3, and
> i've read that new collectives haven't any tag.
>
> Correct.
>
> > So all collective operations must follow the ordering rules for
> collective calls.
>
> Also correct.
>
> > From what i understand, this means that i can't use:
> >
> > MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast
> > MPI_IBcast(MPI_COMM_WORLD, request_2) // second Bcast
>
> No, not quite right. You can have multiple outstanding ibcast's -- they'll
> just be satisfied in the same order in all participating MPI processes.
>
> > but is it possible to do this:
> >
> > MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast
> > MPI_IReducet(MPI_COMM_WORLD, request_2) // othwer collective
>
> Correct -- this is also possible.
>
> More generally, you can have multiple outstanding non-blocking collectives
> on a single communicator -- it doesn't matter if they are the same or
> different collective operations. They will each be unique instances and will
> be satisfied in order.
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
> _______________________________________________
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> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>

-- 
Ing. Gabriele Fatigati
Parallel programmer
CINECA Systems & Tecnologies Department
Supercomputing Group
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it                    Tel:   +39 051 6171722
g.fatigati [AT] cineca.it