I've been speaking off line to Jonathan Dursi about this problem. And it does seems to be a bug.
The same problem crops up in a simplified 1d only case (test case attached). In this instance the specification seems to be comprehensible - looking at the pdf copy of MPI-2.2 spec, p92-93, the definition of cyclic gives MPI_LB=0, MPI_UB=gsize*ex. Test case is creating a data type for an array of 10 doubles, cyclicly distributed across two processes with a block size of 1. Expected extent is 10*extent(MPI_DOUBLE) = 80. Results for OpenMPI v 1.4.4: $ mpirun -np 2 ./testextent1d Rank 0, size=40, extent=80, lb=0 Rank 1, size=40, extent=88, lb=0 Can anyone else confirm this? Thanks Richard On Sunday, 15 July, 2012 at 6:21 PM, Richard Shaw wrote: > Hello, > > I'm getting thoroughly confused trying to work out what is the correct extent > of a block-cyclic distributed array type (created with > MPI_Type_create_darray), and I'm hoping someone can clarify it for me. > > My expectation is that calling MPI_Get_extent on this type should return the > size of the original, global, array in bytes, whereas MPI_Type_size gives the > size of the local section. This isn't really clear from the MPI 2.2 spec, but > from reading around it sound like that's the obvious thing to expect. > > I've attached a minimal C example which tests this behaviour, it creates a > type which views a 10x10 array of doubles, in 3x3 blocks with a 2x2 process > grid. So my expectation is that the extent is 10*10*sizeof(double) = 800. > I've attached the results from running this below. > > In practice both versions of OpenMPI (v1.4.4 and v1.6) I've tested don't give > the behaviour I expect. It gives the correct type size on all processes, but > only the rank 0 process gets the expected extent, all the others get a > somewhat higher value. As a comparison IntelMPI (v4.0.3) does give the > expected value for the extent (included below). > > I'd be very grateful if someone could explain what the extent means for a > darray type? And why it isn't the global array size? > > Thanks, > Richard > > > > == OpenMPI (v1.4.4 and 1.6) == > > $ mpirun -np 4 ./testextent > Rank 0, size=288, extent=800, lb=0 > Rank 1, size=192, extent=824, lb=0 > Rank 2, size=192, extent=1040, lb=0 > Rank 3, size=128, extent=1064, lb=0 > > > > == IntelMPI == > > $ mpirun -np 4 ./testextent > Rank 0, size=288, extent=800, lb=0 > Rank 1, size=192, extent=800, lb=0 > Rank 2, size=192, extent=800, lb=0 > Rank 3, size=128, extent=800, lb=0 > > > > > Attachments: > - testextent.c >
testextent1d.c
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