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Subject: Re: [OMPI users] 100% CPU doing nothing!?
From: Terry Frankcombe (terry_at_[hidden])
Date: 2009-04-21 23:19:57


On Tue, 2009-04-21 at 19:19 -0700, Ross Boylan wrote:
> I'm using Rmpi (a pretty thin wrapper around MPI for R) on Debian Lenny
> (amd64). My set up has a central calculator and a bunch of slaves to
> wich work is distributed.
>
> The slaves wait like this:
> mpi.send(as.double(0), doubleType, root, requestCode, comm=comm)
> request <- request+1
> cases <- mpi.recv(cases, integerType, root, mpi.any.tag(),
> comm=comm)
>
> I.e., they do a simple send and then a receive.
>
> It's possible there's no one to talk to, so it could be stuck at
> mpi.send or mpi.recv.
>
> Are either of those operations that should chew up CPU? At this point,
> I'm just trying to figure out where to look for the source of the
> problem.

The short response is: why do you not want it to use the whole CPU
while waiting?

There's some discussion starting here:
<http://www.open-mpi.org/community/lists/users/2008/04/5457.php>

If you really want to make your application run slower, you can yield
the CPU when not doing much:
<http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded>

Ciao
Terry

-- 
Dr. Terry Frankcombe
Research School of Chemistry, Australian National University
Ph: (+61) 0417 163 509    Skype: terry.frankcombe