[Beowulf] Using Autoparallel compilers or Multi-Threaded libraries with MPI

[Greg Lindahl]

On Mon, Dec 03, 2007 at 10:11:51AM +0100, H?kon Bugge wrote:

> But 
> there are cases where you cannot; a) the 
> "decomposition parallel efficiency" is not good 
> enough or b) the processes need a huge (shared) table.

You can accomplish (b) using a mmaped file, which is much easier than
hybrid programming. I agree that (a) is theoretically useful, but I
have only once seen a benchmark situation where (a) was the case. I
have seen several situations where a hybrid code had a 1D MPI
decomposition and "needed" OpenMP for more scaling, but could have
been a pure MPI 2D or 3D code, with less complexity than the hybrid
code.

-- greg