On Jul 11, 2007, at 10:14 PM, Pedro Petrovitch wrote:
> Thanks for the answer... It actually brought me another question: can
> different implementations of MPI have high difference on execution
> times?
Compare MPI to any other program (say, BLAS). Will different
implementations of BLAS have high differences in execution times? It
depends on who's doing the implementing. It also depends on what you
consider "high difference".
In any case, the key to MPI is scalability and architecture/hardware
support. For example, an MPI implementation can do a good job with
the general case, but be poor at doing collective operations or
scatter/gather. Or one MPI implementation may take advantage of some
specialized hardware details—for example, on an SGI Altix, the SGI
MPI implementation will *probably* kick the tail of other MPI
implementations that are not specifically tuned to the Altix. Does
that mean that a given test program will take an hour with LAM and
half a second with SGI's MPI? Probably not. Does that mean that SGI's
can shave a couple minutes off of a complex program that runs for an
hour under LAM? Quite possibly. Can you take SGI's implementation and
expect the same improvement on a large Sun node? Absolutely not.
~Kyle
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