On Wed, May 22, 2013 at 12:23:36PM -0400, Eric Chamberland wrote: > On 05/22/2013 11:33 AM, Tom Rosmond wrote: > >Thanks for the confirmation of the MPIIO problem. Interestingly, we > >have the same problem when using MPIIO in INTEL MPI. So something > >fundamental seems to be wrong. > > > > I think but I am not sure that it is because the MPI I/O (ROMIO) > code is the same for all distributions... > > It has been written by Rob Latham.
Hello! Rajeev wrote it when he was in grad school, then he passed the torch to Rob Ross when he was a post-doc at Argonne, and now I've been the caretaker for the last mumble-mumble years. (now if i could only find some other sucker....) Tom, Eric: I have recently fixed this bug for some cases. I don't know when OpenMPI will re-sync with ROMIO (it's getting harder and harder to keep ROMIO as "the standalone MPI-IO implementation") but it should be straightforward to pick up that change (it's this one: http://git.mpich.org/mpich.git/blobdiff/2de997d9b3e94bad01d5f46d76f163d71e2bd7bd..7d44307f269cae96118beb19760221aff99bd74a:/src/mpi/romio/adio/common/ad_read.c) The functional descriptions for ROMIO are indeed "integer count of some datatype", but one can still use that to say "write a billion doubles". ROMIO handles this internally with as many calls to the write(2) system call as it takes to complete. If you try to get fancy and make a struct of three thousand megabyte-sized MPI_CONTIG types, MPICH will blow up. I haven't tested against OpenMPI. But basic types should be ok, now. ==rob -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA
