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Subject: Re: [OMPI users] trouble using --mca mpi_yield_when_idle 1
From: douglas.guptill_at_[hidden]
Date: 2008-12-12 15:46:36


Hello Jeff:

On Fri, Dec 12, 2008 at 08:37:14AM -0500, Jeff Squyres wrote:

> FWIW, Open MPI does have on its long-term roadmap to have "blocking"
> progress -- meaning that it'll (probably) spin aggressively for a
> while and if nothing "interesting" is happening, it'll go into a
> blocking mode and let the process block in some kind of OS call.
>
> Although we have some interesting ideas on how to do this, it's not
> entirely clear when we'll get this done. There's been a few requests
> for this kind of feature before, but not a huge demand.

Please count me as wanting that feature. And it would be nice - for
our application - to block immediately.

> This is probably because most users running MPI jobs tend to devote
> the entire core/CPU/server to the MPI job and don't try to run other
> jobs concurrently on the same resources.

Our situation is different. While our number-cruncher application is
running, we would like to be able to do some editing, compiling,
post-processing.

I once ran three jobs, hence 6 processes, on our 4-cpu system, and was
unable to ssh into the machine. Or maybe I did not wait long
enough...

The number-cruncher has two processes, and each needs intermediate
results from the other, inside a
  do i=1,30000
  enddo

As I mentioned earlier, most of the time, only one process is
executing, and the other is waiting for results. My guess is that,
with the blocking feature you describe, I could double the number of
number-cruncher jobs running at one time, thus doubling throughput.

Regards,
Douglas.

-- 
  Douglas Guptill                       
  Research Assistant, LSC 4640          email: douglas.guptill_at_[hidden]
  Oceanography Department               fax:   902-494-3877
  Dalhousie University
  Halifax, NS, B3H 4J1, Canada