[Mpi-forum] MPI "Allocate receive" proposal

Anthony Skjellum tony at cis.uab.edu
Mon Aug 26 14:29:01 CDT 2013

If I understand this correctly, some of us suggested allocate-on-receive, free-on-send mode,
but left this out in MPI-1.  I advocated this type of reactive semantics ... That's how
the Reactive Kernel worked at Caltech for instance...  Allowing for MPI to choose efficient memory for messages of some sizes
can provide nice properties, provided the memory is good to compute in.  There are always concerns about starvation from holding
the messages too long :-)  

I'd like to see this get full consideration.  It could be a big help in exascale to have fine-grain computing.

For instance, could we not get zero-copy unexpected short messages in this way?


----- Original Message -----
From: "David Goodell (dgoodell)" <dgoodell at cisco.com>
To: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
Sent: Monday, August 26, 2013 1:23:04 PM
Subject: Re: [Mpi-forum] MPI "Allocate receive" proposal

JeffH, please read the slides for motivation and performance opportunities, esp. the big red bullets on #2, #6, and #7.


On Aug 26, 2013, at 1:05 PM, Jeff Hammond <jeff.science at gmail.com> wrote:

> When does this actually improve performance?  If memory is a limiting factor, it merely eliminates a function call.  If memory is limiting, I don't see how doing extra ping-pong to keep from hitting OOM errors is noticeable.
> JeffS and Dave: What's the use case?  So far, I fail to see how this is more than icing.
> Jeff
> On Mon, Aug 26, 2013 at 12:55 PM, Sur, Sayantan <sayantan.sur at intel.com> wrote:
> This is a good feature to have in general that improves performance, although the devil is in the details.
> What is the app trying to do when it finds itself in the quandary of having to accept any sized message (probably from any source as well?). It appears to me that the kind of app that is looking for this feature, or could benefit from this feature is really looking for a many-to-one (or one-to-one, many-to-many) reliably connected stream. It is likely that the app that benefits significantly from this feature will be repeatedly using this call to fetch differing amounts of data each time.
> A few meetings ago, Bill mentioned that it would be good to think of the standard as a whole and not get bogged down in narrow use-cases. He proposed that a streaming model be added to MPI P2P communications. Can this use-case be included in that model?
> Thanks,
> Sayantan
> > -----Original Message-----
> > From: mpi-forum [mailto:mpi-forum-bounces at lists.mpi-forum.org] On
> > Behalf Of Jeff Squyres (jsquyres)
> > Sent: Monday, August 26, 2013 8:11 AM
> > To: MPI Forum list
> > Subject: [Mpi-forum] MPI "Allocate receive" proposal
> >
> > Dave Goodell and I have a proposal that we've socialized a bit around with
> > other Forum members, and would now like larger Forum feedback.  I'll be
> > presenting the attached slides on the concept of an "allocate receive" in
> > Madrid (3:30-4pm on Thursday).
> >
> > There's no text or ticket yet; this is an idea that we want to get feedback on
> > before working up a full proposal.
> >
> > --
> > Jeff Squyres
> > jsquyres at cisco.com
> > For corporate legal information go to:
> > http://www.cisco.com/web/about/doing_business/legal/cri/
> _______________________________________________
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> -- 
> Jeff Hammond
> jeff.science at gmail.com
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Anthony Skjellum, PhD 
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Department of Computer and Information Sciences 
Director, UAB Center for Information Assurance and Joint Forensics Research ("The Center") 
University of Alabama at Birmingham 
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