Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: Re: [OMPI users] MPI_Comm_spawn, caller uses CPU while waiting for spawned processes
From: Nicolas Bock (nicolasbock_at_[hidden])
Date: 2009-12-04 12:58:11

On Fri, Dec 4, 2009 at 10:29, Eugene Loh <Eugene.Loh_at_[hidden]> wrote:

> Nicolas Bock wrote:
> On Fri, Dec 4, 2009 at 10:10, Eugene Loh <Eugene.Loh_at_[hidden]> wrote:
>> Yield helped, but not as effectively as one might have imagined.
> Yes, that's the impression I get as well, the master process might be
> yielding, but it doesn't appear to be a lot. Maybe I should do this
> differently to avoid this CPU usage in master. All I really want is to
> execute another process somewhere on a free node in my MPI universe, wait
> for it to be done and go on. From my limited understanding of MPI,
> MPI_Comm_spawn() and MPI_Barrier() seemed just like what I needed, but as I
> said, maybe there are other ways to do this.
> I think you might observe a world of difference if the master issued some
> non-blocking call and then intermixed MPI_Test calls with sleep calls. You
> should see *much* more subservient behavior. As I remember, putting such
> passivity into OMPI is on somebody's to-do list, but just not very high.

Hi Eugene,

could you give me more details? I can't figure out how to do this. I could
see that one way to implement what you are describing is:

in slave.c:
MPI_Send() to rank 0

in master.c
MPI_IRecv() from the spawned processes
while (1) { MPI_Test(); }

I can't figure out how to find the ranks that MPI_Comm_spawn() used. What's
the source argument in MPI_IRecv() supposed to be?

Thanks, nick