[Mpi3-hybridpm] Fwd: Re: First cut at slides

Jeff Hammond jhammond at alcf.anl.gov
Mon Jul 1 11:06:16 CDT 2013

My 10 am meeting is running over (again) so I will once again miss this or be extremely late.



----- Original Message -----
From: "Pavan Balaji" <balaji at mcs.anl.gov>
To: mpi3-hybridpm at lists.mpi-forum.org
Sent: Monday, July 1, 2013 11:03:49 AM
Subject: [Mpi3-hybridpm] Fwd: Re:  First cut at slides

FYI,  Here are the slides we are discussing.

-------- Original Message --------
Subject: Re: [Mpi3-hybridpm] First cut at slides
Date: Sat, 22 Jun 2013 13:27:59 +0000
From: Jeff Squyres (jsquyres) <jsquyres at cisco.com>
To: Pavan Balaji <balaji at mcs.anl.gov>
CC: <mpi3-hybridpm at lists.mpi-forum.org> <mpi3-hybridpm at lists.mpi-forum.org>

On Jun 22, 2013, at 9:03 AM, Pavan Balaji <balaji at mcs.anl.gov> wrote:

> Thanks.  The slides seem to be confusing collective vs. synchronizing. I think you mean to say that INIT/FINALIZE are always collective, and they *might* be synchronizing (though we expect most implementations to not be synchronizing when they are not actually initializing or finalizing).

How so?  I thought slide 13 was fairly explicit about that:

- INIT and FINALIZE still collective
    - Continue to not specify if they synchronize or not

(although to be fair, I'm not sure if that is a local edit or not -- I 
can't remember offhand what was in the last version of the PPTX I sent 
out, so I've attached a current copy of the slides; see slide 13)

> Also, doesn't IS_THREAD_MAIN need to be thread safe as well, like QUERY_THREAD_LEVEL?

Yes, I missed that -- fixed.

> I agree with JeffH that CONNECT/DISCONNECT is not a problem.  MPI cannot actually finalize in the first call to MPI_FINALIZE in your example, since the ref-count didn't reach zero.

I guess my point is that process A must wait for the *actual* 
finalization in process B (which is the 2nd one), and if Finalize 
synchronizes (which most.. but not all.. MPI implementations do), then A 
will block until B calls the 2nd Finalize.

But I think I'm coming to the conclusion that if you want to not be 
affected by Finalize-possibly-blocking semantics, then you should just 

Jeff Squyres
jsquyres at cisco.com
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Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
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