Computing the Delta-Eddington Approximation for Solar Radiation With Hardware Accelerators: Performance and Programmability on GPUs, FPGAs, and Microprocessors.

The raddedmx routine is a computationally expensive portion of the short-wave radiation calculations in the NCAR Community Climate System Model (CCSM). The routine calculates the Delta-Eddington Approximation on columns of independent data, and executes a high number of floating point operations per byte of data accessed, making it a good candidate for hardware acceleration. We compare several implementation strategies for the raddedmx computation on two hardware acceleration platforms, Graphics Processing Units (GPUs) and Field Programmable Gate Arrays (FPGAs), and analyze the computational speedups that can be realized in addition to programmability and the software engineering effort required on the different platforms. Implementations are found that are able to realize computational speedups in excess of 400x, and overall speedups in excess of 30x including data transfer overhead, versus the microprocessor of the host system. We discuss limitations of the various platforms and implementations, additional features that could improve performance, and the possibility of extending the work to accelerate other portions of the CCSM.