Porting and optimizing HYDRO to new platforms and programming paradigms – lessons learnt

The purpose of low-level benchmarks is to measure certain important characteristics of the target computer system such as arithmetic and communication rates and overheads. They are synthetic in the sense that each is designed to measure a particular architectural feature of the computer. In contrast to higher-level kernel and application benchmarks, they solve no real problem and they don’t exhibit properties of real production codes which scientific computer developers experiment daily with. On the other hand real application codes can be very complex and can use multiple specific algorithms. It can be very difficult or costly to port the code to a specific processor or to a new architecture. Since HYDRO has been extracted from a real code (RAMSES [1]), it occurred to us that it will be a good candidate for benchmarking purposes. HYDRO includes classical algorithms we can find in many applications codes for Tier-0 systems. It has been written in several versions including Fortran and C in order to experiment many new ways of parallelism and to adapt it easily to new architectures that are emerging. In this paper, we described the different versions of HYDRO we have developed using classical or new parallel programming technics or paradigms. We also synthetized the lessons that could be learned from this work, the difficulties that we have encountered in porting the application, the ease of use and the maturity of the new parallel programming paradigms and the significant improvements in terms of performance that could be obtained