New Life in Dusty Decks: Results of Porting a CM Fortran Based Aeroacoustic Model to High Performance Fortran

The High Performance Fortran language is a 'standard by consensus', developed by individuals and vendors in the high performance computing industry, to provide a low barrier entry to parallel computing. It promises to be an easier to use development environment for distributed memory computing platforms compared to the programming complexity required by message passing libraries such as PVM and MPI. HPF promises much and is still in its infancy. Since HPF was developed in part based on experiences gained with early parallel Fortran compilers such as Thinking Machines CM Fortran, we decided to test the effectiveness of HPF with today's generation of HPF compilers by porting a complex existing model code originally developed using CM Fortran. The model code that we selected is a hybrid computational aeroacoustics code that solves the 3D, time-dependent Euler equations in the near flow field and uses a moving surface Kirchhoff's formula to predict the far field sound radiating from turbofan engine inlets. The original CM Fortran model code was developed on a Thinking Machines CM5. The extensive production research use of this model, using varying grid sizes, provides excellent benchmarks with which to compare the HPF port. Two HPF compilers were selected in the porting effort -- The Portland Group's (PGI) pghpf and the xlhpf compiler from IBM. IBM's xlhpf does not implement some elements of the HPF subset while PGI's offering provides several full-HPF extensions. porting efforts using each compiler exposed the strengths and weaknesses of each. Porting this complex code exposed many of the growing pains associated with the current generation of compilers. Critical sections of the code will be explained and these critical areas of the conversion effort will be discussed. Where necessary we will demonstrate how different porting strategies affected the performance of the code. Finally we will present how the ported code ran, using a varying number of processors, on an IBM SP2 and an SGI Origin 2000. While the current simple port does not match the speed of a CM-5, we hope further porting efforts and improved compiler technology will enable us to eventually match and then surpass CM-5 performance levels. With the shutdown of the NCSA CM-5 and the eventual removal and failure of the remaining Thinking Machines hardware currently installed, this effort will demonstrate that investments in CM Fortran code need not be abandoned and that new life can be breathed into those dusty decks.