[Lustre-discuss] MPI-IO / ROMIO support for Lustre

[Mark Dixon]

On Fri, 5 Nov 2010, Rob Latham wrote:
...
> hello!  I'm "the ROMIO guy".

Hi Rob, thanks for replying - good to know the background and that OpenMPI 
isn't being left behind!

...
> ROMIO uses these fcntl locks in one place on Lustre: the noncontiguous
> write path uses an optimization called "data sieving", which is a good
> optmization except there is a read-modify-write step.  If two
> processes simultaneously read-modify-write the same region, who wins?
> We guard against this with an fcntl lock.  Or by disabling data
> sieving writes.

Assuming I do not disable data sieving, which of the following options 
will most likely give me correct behaviour?

1) Enable Lustre's cluster-wide coherent fcntl locks.

2) Cheat, and enable Lustre's (cheaper) fcntl locks that are only coherent 
on an individual computer, on the assumption that Lustre's own internal 
locking mechanisms will "do the right thing".

...
> you can take the romio distribution from the recent MPICH2-1.3.0
> release and build that against an existing MPI library.   You have to
> get the link order right, but if you are dedicated to using an old MPI
> version for other reasons, linking in a new ROMIO version might be the
> way to go.
...

Happily, I'm due to update my MPIs soon :)

Thanks again,

Mark
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Mark Dixon                       Email    : m.c.dixon at leeds.ac.uk
HPC/Grid Systems Support         Tel (int): 35429
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