First off, 1.4.4 is fairly ancient. You might want to try upgrading to 1.6.3.
Second, you might want to use non-blocking receives for B such that you can MPI_WAITALL, or perhaps MPI_WAITSOME or MPI_WAITANY to wait for some/all of the values to arrive in B. This keeps any looping down in MPI (i.e., as close to the hardware as possible). On Jan 25, 2013, at 3:21 PM, Jeremy McCaslin <jomccas...@gmail.com> wrote: > Hello, > > I am trying to figure out the most appropriate MPI calls for a certain > portion of my code. I will describe the situation here: > > Each cell (i,j) of my array A is being updated by a calculation that depends > on the values of 1 or 2 of the 4 possible neighbors A(i+1,j), A(i-1,j), > A(i,j+1), and A(i,j-1). Say, for example, A(i,j)=A(i-1,j)*A(i,j-1). The > thing is, the values of the neighbors A(i-1,j) and A(i,j-1) cannot be used > until an auxiliary array B has been updated from 0 to 1. The values B(i-1,j) > and B(i,j-1) are changed from 0 -> 1 after the values A(i-1,j) and A(i,j-1) > have been communicated to the proc that contains cell (i,j), as cells (i-1,j) > and (i,j-1) belong to different procs. Here is pseudocode for how I have the > algorithm implemented (in fortran): > > do while (B(ii,jj,kk).eq.0) > if (probe_for_message(i0,j0,k0,this_sc)) then > my_ibuf(1)=my_ibuf(1)+1 > A(i0,j0,k0)=this_sc > B(i0,j0,k0)=1 > end if > end do > > The function 'probe_for_message' uses an 'MPI_IPROBE' to see if > 'MPI_ANY_SOURCE' has a message for my current proc. If there is a message, > the function returns a true logical and calls 'MPI_RECV', receiving > (i0,j0,k0,this_sc) from the proc that has the message. This works! My > concern is that I am probing repeatedly inside the while loop until I receive > a message from a proc such that ii=i0, jj=j0, kk=k0. I could potentially > call MPI_IPROBE many many times before this happens... and I'm worried that > this is a messy way of doing this. Could I "break" the mpi probe call? Are > there MPI routines that would allow me to accomplish the same thing in a more > formal or safer way? Maybe a persistent communication or something? For > very large computations with many procs, I am observing a hanging situation > which I suspect may be due to this. I observe it when using openmpi-1.4.4, > and the hanging seems to disappear if I use mvapich. Any > suggestions/comments would be greatly appreciated. Thanks so much! > > -- > JM _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
