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Subject: Re: [OMPI users] How to start MPI_Spawn child processes early?
From: Richard Treumann (treumann_at_[hidden])
Date: 2010-01-27 18:27:14


I cannot resist:

Jaison -

The MPI_Comm_spawn call specifies what you want to have happen. The child
launch is what does happen.

If we can come up with a way to have things happen correctly before we know
what it is that we want to have happen, the heck with this HPC stuff. Lets
get together and place stock orders on yesterday's market.

Just joking - Ralph's suggestion about launching all parts of the
application up front and then using JOIN or ACCEPT/CONNECT will work. I
also agree with his skepticism about the problem. Most applications that
are worth running in parallel take long enough so the time it takes to
spawn should be barely noticeable.

Are you using parallelism for something that only takes a few seconds and
if so, why not just do it with a serial run?

Dick Treumann - MPI Team
IBM Systems & Technology Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846 Fax (845) 433-8363

users-bounces_at_[hidden] wrote on 01/27/2010 06:07:43 PM:

> [image removed]
>
> Re: [OMPI users] How to start MPI_Spawn child processes early?
>
> Ralph Castain
>
> to:
>
> Open MPI Users
>
> 01/27/2010 06:09 PM
>
> Sent by:
>
> users-bounces_at_[hidden]
>
> Please respond to Open MPI Users
>
> I can't imagine how you would do that - only thing I can think of
> would be to start your "child" processes as one job, then start your
> "parent" processes and have them do an MPI_Comm_join with the child job.
>
> That said, I can't imagine that comm_spawn is -that- slow to make
> much difference to an HPC application! At least, not in anything
> I've measured.
>
> On Jan 27, 2010, at 3:24 PM, Jaison Paul wrote:
>
> > Hi, I am just reposting my early query once again. If anyone one
> can give some hint, that would be great.
> >
> > Thanks, Jaison
> > ANU
> >
> > Jaison Paul wrote:
> >> Hi All,
> >>
> >> I am trying to use MPI for scientific High Performance (hpc)
> applications. I use MPI_Spawn to create child processes. Is there a
> way to start child processes early than the parent process, using
MPI_Spawn?
> >>
> >> I want this because, my experiments showed that the time to spawn
> the children by parent is too long for HPC apps which slows down the
> whole process. If the children are ready when parent application
> process seeks for them, that initial delay can be avoided. Is there
> a way to do that?
> >>
> >> Thanks in advance,
> >>
> >> Jaison
> >> Australian National University
> >> _______________________________________________
> >> users mailing list
> >> users_at_[hidden]
> >> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
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