CRPC-TR93365-S

Title:    Value-based Distributions and Alignments in Fortran D

Authors:  Reinhard von Hanxleden, Ken Kennedy, Joel Saltz

Date:     December 1993, revised May 1994


Of the authors listed above, please indicate which are:

  Minority authors:

  Female authors:    

  Student authors:   Reinhard von Hanxleden


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Abstract:

Compiling irregular applications written in a data-parallel
language,like Fortran D or High Performance Fortran (HPF), presents a
challenge of growing importance. A major component of data-parallel
programming is the data mapping, i.e., data distribution and
alignment. Mappings may be either regular, in which case they
correspond to simple functions between array indices and owning
processors, or irregular. Regular mappings can already be specified
fairly conveniently, with keywords such as BLOCK or CYCLIC. However,
the mechanisms proposed for irregular mappings so far require the
programmer to go down to a very low level, for example by specifying
explicit mapping arrays or mapping functions. For irregular problems,
this makes it difficult to achieve good load balance or low storage
and communication requirements without sacrificing programming
convenience.

Value-based mappings extend classical, index-based mappings to express
for example the locality characteristics of an underlying physical
problem. This gives the compiler an opportunity to improve both inter-
and intra-processor locality, resulting in better performance and
scalability, even when this locality is not inherent in the original
data structures and access patterns.

This paper reports on the experience gained from implementing
value-based mappings in a Fortran 77D compiler prototype. We propose a
natural extension of index-based mappings as already present in
Fortran D and HPF. This paper addresses the compilation issues
involved and makes a quantitative comparison of index and value-based
mappings for a Molecular Dynamics application and an Unstructured Mesh
kernel.


Publication History:

  Submitted to: The Journal of Programming Languages, Special Issue 
                on Compiling and Run-time Issues for Distributed Address 
                Space Machines

  Published in: