OpenCL - An effective programming model for data parallel computations at the Cell Broadband Engine

Current processor architectures are diverse and heterogeneous. Examples include multicore chips, CPUs and the Cell Broadband Engine (CBE). The recent Open Compute Language (OpenCL) standard aims at efficiency and portability. This paper explores its efficiency when implemented on the CBE, without using CBE-specific features such as explicit asynchronous memory transfers. We based our experiments on two applications: matrix multiplication, and the client side of the Einstein@Home distributed computing project. Both were programmed in OpenCL, and then translated to the CBE. For matrix multiplication, we deployed different levels of OpenCL performance optimization, and observed that they pay off on the CBE. For the Einstein@Home application, our translated OpenCL version achieves almost the same speed as a native CBE version. Another main contribution of the paper is a proposal for an additional memory level in OpenCL, called static local memory. With little programming expense, it can lead to significant speedups such as factor seven for reduction. Finally, we studied two versions of the OpenCL to CBE mapping, in which the PPE component of the CBE does or does not take the role of a compute unit.