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Subject: Re: [OMPI users] nonblocking MPI_File_iwrite() does block?
From: Christoph Rackwitz (rackwitz_at_[hidden])
Date: 2009-11-27 07:45:19


Rob Latham wrote:
> If the other processors need header data, perhaps rank 0 can broadcast
> it to everyone else?

That's what happens, when *reading* that file back to continue
number-crunching. When writing, rank 0 is also the only one to write a
header, and then each rank writes their parts of the matrices.

> Is it OK to mention MPICH2 on this list? I did prototype some MPI
> extensions that allowed ROMIO to do true async I/O (at least as far
> as the underlying operating system supports it). If you really need
> to experiment with async I/O, I'd love to hear your experiences.

I don't really need to, I think. I can't say I have had any experience
either. It would have been a great demo of real-world implementation and
performance, but the convenience of the APIs themselves is good enough.
I'll try and see how much split-collective operations will bring,
performance-wise.

Thanks