Evaluation of a Cray performance tool using a large hydrodynamics code

This paper will discuss one of these automatic tools that has been developed recently by Cray Research, Inc. for use on its parallel supercomputer. The tool is called ATEXPERT; when used in conjunction with the Cray Fortran compiling system, CF77, it produces a parallelized version of a code based on loop-level parallelism, plus information to enable the programmer to optimize the parallelized code and improve performance. The information obtained through the use of the tool is presented in an easy-to-read graphical format, making the digestion of such a large quantity of data relatively easy and thus, improving programmer productivity. In this paper we address the issues that we found when the took a large Los Alamos hydrodynamics code, PUEBLO, that was highly vectorizable, but not parallelized, and using ATEXPERT proceeded to parallelize it. We show that through the advice of ATEXPERT, bottlenecks in the code can be found, leading to improved performance. We also show the dependence of performance on problem size, and finally, we contrast the speedup predicted by ATEXPERT with that measured on a dedicated eight-processor Y-MP