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Subject: Re: [OMPI users] Using MPI_Put/Get correctly?
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-12-15 21:18:48

Is there a reason to convert your code from send/receive to put/get?

The performance may not be that significantly different, and as you have noted, the MPI-2 put/get semantics are a total nightmare to understand (I personally advise people not to use them -- MPI-3 is cleaning up the put/get semantics a LOT).

On Dec 15, 2010, at 3:15 PM, Grismer, Matthew J Civ USAF AFMC AFRL/RBAT wrote:

> I am trying to modify the communication routines in our code to use
> MPI_Put's instead of sends and receives. This worked fine for several
> variable Put's, but now I have one that is causing seg faults. Reading
> through the MPI documentation it is not clear to me if what I am doing
> is permissible or not. Basically, the question is this - if I have
> defined all of an array as a window on each processor, can I PUT data
> from that array to remote processes at the same time as the remote
> processes are PUTing into the local copy, assuming no overlaps of any of
> the PUTs?
> Here are the details if that doesn't make sense. I have a (Fortran)
> array QF(6,2,N) on each processor, where N could be a very large number
> (100,000). I create a window QFWIN on the entire array on all the
> processors. I define MPI_Type_indexed "sending" datatypes (QFSND) with
> block lengths of 6 that send from QF(1,1,*), and MPI_Type_indexed
> "receiving" datatypes (QFREC) with block lengths of 6 the receive into
> QF(1,2,*). Here * is non-repeating set of integers up to N. I create
> groups of processors that communicate, where these groups will all
> exchange QF data, PUTing local QF(1,1,*) to remote QF(1,2,*). So,
> processor 1 is PUTing QF data to processors 2,3,4 at the same time 2,3,4
> are putting their QF data to 1, and so on. Processors 2,3,4 are PUTing
> into non-overlapping regions of QF(1,2,*) on 1, and 1 is PUTing from
> QF(1,1,*) to 2,3,4, and so on. So, my calls look like this on each
> processor:
> assertion = 0
> call MPI_Win_post(group, assertion, QFWIN, ierr)
> call MPI_Win_start(group, assertion, QFWIN, ierr)
> do I=1,neighbors
> call MPI_Put(QF, 1, QFSND(I), NEIGHBOR(I), 0, 1, QFREC(I), QFWIN,
> ierr)
> end do
> call MPI_Win_complete(QFWIN,ierr)
> call MPI_Win_wait(QFWIN,ierr)
> Note I did define QFREC locally on each processor to properly represent
> where the data was going on the remote processors. The error value
> ierr=0 after MPI_Win_post, MPI_Win_start, MPI_Put, and MPI_Win_complete,
> and the code seg faults in MPI_Win_wait.
> I'm using Open MPI 1.4.3 on Mac OS X 10.6.5, built with Intel XE (12.0)
> compilers, and running on just 2 (internal) processors of my Mac Pro.
> The code ran normally with this configuration up until the point I put
> the above in. Several other communications with MPI_Put similar to the
> above work fine, though the windows are only on a subset of the
> communicated array, and the origin data is being PUT from part of the
> array that is not within the window.
> _____________________________________________________
> Matt
> _______________________________________________
> users mailing list
> users_at_[hidden]

Jeff Squyres
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