Re: [OMPI users] User-built OpenMPI 3.0.1 segfaults when storing into an atomic 128-bit variable

On Thu, May 3, 2018 at 11:23 PM, Nathan Hjelm wrote: > Not saying we won't change the behavior. Just saying the user can't expect > a particular alignment as there is no guarantee in the standard. In Open > MPI we just don't bother to align the pointer so right now so it

Re: [OMPI users] User-built OpenMPI 3.0.1 segfaults when storing into an atomic 128-bit variable

Not saying we won't change the behavior. Just saying the user can't expect a particular alignment as there is no guarantee in the standard. In Open MPI we just don't bother to align the pointer so right now so it naturally aligns as 64-bit. It isn't about wasting memory. Also remember that by

Re: [OMPI users] User-built OpenMPI 3.0.1 segfaults when storing into an atomic 128-bit variable

Given that this seems to break user experience on a relatively frequent basis, I’d like to know the compelling reason why MPI implementers aren’t willing to do something utterly trivial to fix it. And don’t tell me that 16B alignment wastes memory versus 8B alignment. Open-MPI “wastes” 4B

Re: [OMPI users] User-built OpenMPI 3.0.1 segfaults when storing into an atomic 128-bit variable

That is probably it. When there are 4 ranks there are 4 int64’s just before the user data (for PSCW). With 1 rank we don’t even bother, its just malloc (16-byte aligned). With any other odd number of ranks the user data is after an odd number of int64’s and is 8-byte aligned. There is no

Re: [OMPI users] User-built OpenMPI 3.0.1 segfaults when storing into an atomic 128-bit variable

Martin, You say that you allocate shared memory, do you mean shared memory windows? If so, this could be the reason: https://github.com/open-mpi/ompi/issues/4952 The alignment of memory allocated for MPI windows is not suitable for 128bit values in Open MPI (only 8-byte alignment is