Utz Bacher

directCell: hybrid systems with tightly coupled accelerators

The Cell Broadband Engine® (Cell/B.E.) processor is a hybrid IBM PowerPC® processor. In blade servers and PCI Express® card systems, it has been used primarily in a server context, with Linux® as the operating system. Because neither Linux as an operating system nor a PowerPC processor-based architecture is the preferred choice for all applications, some installations use the Cell/B.E. processor in a coupled hybrid environment, which has implications for the complexity of systems management, the programming model, and performance. In the directCell approach, we use the Cell/B.E. processor as a processing device connected to a host via a PCI Express link using direct memory access and memory-mapped I/O (input/output). The Cell/B.E. processor functions as a processor and is perceived by the host like a device while maintaining the native Cell/B.E. processor programming approach. We describe the problems with the current practice that led us to the directCell approach. We explain the challenge in programming, execution control, and operation on the accelerators that were faced during the design and implementation of a prototype and present solutions to overcome them. We also provide an outlook on where the directCell approach promises to better solve customer problems.