[Beowulf] programming multicore clusters

[Greg Lindahl]

On Fri, Jun 15, 2007 at 08:00:24AM -0500, Gerry Creager wrote:

> For the forseeable future, I'm not developing much but will use the 
> hybrid SMP/DM capabilities in WRF.  Takes advantage of SMP availability, 
> and supports message passing between SMP nodes.  I've not used this 
> capability for benchmarking but it appears to offer significant gains.

Gerry, why do you think WRF is going to behave any different from MM5
in this aspect? MM5 slows down in hybrid mode. MPI "takes advantage"
of SMP. In fact, on big SMPs like Origin and Altix, MPI programs are
often faster than shared memory or OpenMP programs, unless you've done
a lot of work on the OpenMP program to improve locality. Why? Because
you're forced to worry about locality in an MPI program all the time.

> As we get more hybrid HPC capabilities planning for this will be more 
> important.

I predict a lot of people will waste a lot of time without seeing a
benefit.

-- greg