Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] MPIIO max record size
From: Rob Latham (robl_at_[hidden])
Date: 2013-07-19 15:30:32

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:

The functional descriptions for ROMIO are indeed "integer count of
some datatype", but one can still use that to say "write a billion

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 Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA