On Jul 28, 2010, at 5:07 PM, Gus Correa wrote: > Still, the alignment under Intel may or may not be right. > And this may or may not explain the errors that Hugo has got. > > FYI, the ompi_info from my OpenMPI 1.3.2 and 1.2.8 > report exactly the same as OpenMPI 1.4.2, namely > Fort dbl prec size: 4 and > Fort dbl prec align: 4, > except that *if the Intel Fortran compiler (ifort) was used* > I get 1 byte alignment: > Fort dbl prec align: 1 > > So, this issue has been around for a while, > and involves both the size and the alignment (in Intel) > of double precision.
Yes, it's quite problematic to try to determine the alignment of Fortran types -- compilers can do different things and there's no reliable way (that I know of, at least) to absolutely get the "native" alignment. That being said, we didn't previously find any correctness issues with using an alignment of 1. > We have a number of pieces of code here where grep shows > MPI_DOUBLE_PRECISION. > Not sure how much of it has actually been active, as there are always > lots of cpp directives to select active code. > > In particular I found this interesting snippet: > > if (MPI_DOUBLE_PRECISION==20 .and. MPI_REAL8==18) then > ! LAM MPI defined MPI_REAL8 differently from MPI_DOUBLE_PRECISION > ! and LAM MPI's allreduce does not accept on MPI_REAL8 > MPIreal_t = MPI_DOUBLE_PRECISION > else > MPIreal_t = MPI_REAL8 > endif This kind of thing shouldn't be an issue with Open MPI, right? FWIW, OMPI uses different numbers for MPI_DOUBLE_PRECISION and MPI_REAL8 than LAM. They're distinct MPI datatypes because they *could* be different. -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
