[Beowulf] Off-the-wall: WRF Model and PS3's (or Cell)

[Cédric Augonnet]

2008/5/16 Gerry Creager <gerry.creager at tamu.edu>:
> Has anyone seen a citation or reference for actually running WRF on a PS3
> cluster?  I've got an itch to deploy a 16-PS3 cluster (gigabit intersinnect
> <sigh>).  That said, it's too much money to squander if there's not some
> indication it'd show improvement over a "normal" cluster.
>
> gerry

Hi Gerry,

I guess this is unlikely that PS3 would be that good for such a task
while having only around 200MB available once the OS is running. In
addition to the network card that is not really adapted for
clustering, the most important aspect is how to get some performance
improvement using the Cell ?

Perhaps i'm just stating something obvious there, but a cell is
nothing but a mere (rather old) PPC  which comes with a bunch of
coprocessors (SPEs), if you do not explicitely port the code so that
it is offloaded on those coprocessors, there is no use in looking at
the Cell. Perhaps there are ways to greatly improve WRF by offloading
some compute intensive parts onto the coprocessors, but it *really*
requires a lot of non-trivial work, and as far as i know (please
correct me if i'm wrong) there is no such work done yet.

However, i have seen that WRF 3.0 should support some "GPU accelerated
microphysics" as an experimental feature; so perhaps some of those
compute intensive parts can be rewrote to be explicitely offloaded on
SPEs instead of GPUs ?

Eventually, PS3 does not seem to fit clustering requirement given how
small is its memory, and the poor network. And even if you were to use
some Blades from IBM (like QS21, with high speed networks and decent
memory size) there is still  a big change that WRF needs a substancial
effort to get the least benefit from running on the Cell. More
generally, in case you did not see those before, Dongarra et al. wrote
some interesting papers about  PS3 clustering [1][2].

Regards,
Cédric

[1] A Rough Guide to Scientific Computing On the PlayStation 3  -
http://www.netlib.org/utk/people/JackDongarra/PAPERS/scop3.pdf
[2] Limitations of the PlayStation 3 for High Performance Cluster
Computing - http://www.netlib.org/lapack/lawnspdf/lawn185.pdf