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

Lombard, David N dnlombar at ichips.intel.com
Tue Dec 4 07:17:48 PST 2007

On Sun, Dec 02, 2007 at 03:51:53PM +0100, Toon Knapen wrote:
> Mark Hahn wrote:
> >>IMHO the hybris approach (MPI+threads) is interesting in case every
> >>MPI-process has lots of local data.
> >
> >yes.  but does this happen a lot?  the appealing case would be threads 
> >that make lots of heavy use of some large data, _but_
> >without needing synchronization/locking.  once you need locking
> >among the threads, message passing starts to catch up.
> Direct solvers (for Finite Elements for instance) need a lot of data. 
> Additionally distributing the matrix generate interfaces (between the 
> different submatrices) which are hard to solve. In such situation, one 
> tries to minimize the number of interfaces (by having one submatrix per 
> MPI-process) and speed up the solving of each submatrix using threads.

Yes, this is my direct experience with hybrid programming.  An automated
domain decomp is used to partition the model, and then threads (either
native or OpenMP) are used within the domain.

David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.

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