THEMIS: Component dependence metadata
		  in adaptive parallel applications

	     Paul H J Kelly, Olav Beckmann and Tony Field
		       Department of Computing
	 Imperial College of Science, Technology and Medicine
		 180 Queen's Gate, London SW7 2BZ, UK
		   Contact email: p.kelly@ic.ac.uk

			    Scott B. Baden
	    Deaprtment of Computer Science and Engineering
		 University of California, San Diego
		     La Jolla, CA 92093-0114, USA

			       May 2001


			       Abstract
			       --------

There  is a conflict  between the  goals of  improving the  quality of
scientific software and improving its performance.   A key issue is to
support  reuse  and re-assembly of   sophisticated software components
without  compromising  performance.  This paper  describes  THEMIS,  a
programming  model and   run   time   library  designed  to    support
cross-component performance optimisation through explicit manipulation
of the computation's iteration space at run-time.

Each component  is augmented  with ``component  dependence metadata'',
which  characterises the  constraints on   its  execution order,  data
distribution and access order.    We show  how this  supports  dynamic
adaptation of each component to  exploit the available resources,  the
context in which its operands are generated, and results are used, and
the evolution of the problem instance.

Using  a   computational  fluid  dynamics    visualisation example  as
motivation,   we show how    component dependence metadata  provides a
framework  in  which  a  number  of interesting  optimisations  become
possible.  Examples include data  placement optimisation, loop fusion,
tiling, memoisation, checkpointing and incrementalisation.