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Subject: Re: [OMPI users] Parallel I/O with MPI-1
From: Robert Latham (robl_at_[hidden])
Date: 2008-07-24 09:15:24


On Wed, Jul 23, 2008 at 02:24:03PM +0200, Gabriele Fatigati wrote:
> >You could always effect your own parallel IO (e.g., use MPI sends and
> receives to coordinate parallel reads and writes), but >why? It's already
> done in the MPI-IO implementation.
>
> Just a moment: you're saying that i can do fwrite without any lock? OpenMPI
> does this?

You use MPI to describe your I/O regions. In fact, these I/O regions
can even overlap (something that you can't do efficiently with
lock-based approaches). Even better, if you do your I/O
"collectively" the MPI library will optimize the heck out of your
accesses.

When I was learning all this way back when, it took me a long time to
get all the details straight (memory types, file views, tiling,
independent vs. collective), but a few readings of the I/O chapter of
"Using MPI-2" set me straight.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Lab, IL USA                 B29D F333 664A 4280 315B