Performance analysis of cell broadband engine for high memory bandwidth applications. Performance Analysis

The Cell Broadband Engine (CBE) is designed to be a general purpose platform exposing an enormous arithmetic performance due to its eight SIMD-only Synergistic Processor Elements (SPEs), capable of achieving 134.4 GFLOPS (16.8 GFLOPS * 8) at 2.1 GHz, and a 64-bit Power Processor Element (PPE). Each SPE has a 256Kb non-coherent local memory, and communicates to other SPEs and main memory through its DMA controller. CBE main memory is connected to all the CBE processor elements (PPE and SPEs) through the Element Interconnect Bus (EIB), which has a 134.4GB/s bandwidth performance peak at half the processor speed. Therefore, CBE platform is suitable to be used by applications using MPI and streaming programming models with a potential high performance peak. In this paper we focus on the communication part of those applications, and measure the actual memory bandwidth that each of the CBE processor components can sustain. We have measured the sustained bandwidth between PPE and memory, SPE and memory, two individual SPEs to determine if this bandwidth depends on their physical location, pairs of SPEs to achieve maximum bandwidth in nearly-ideal conditions, and in a cycle of SPEs representing a streaming kind of computation. Our results on a real machine show that following some strict programming rules, individual SPE to SPE communication almost achieves the peak bandwidth when using the DMA controllers to transfer memory chunks of at least 1024 bytes. In addition, SPE to memory bandwidth should be considered in streaming programming. For instance, implementing two data streams using 4 SPEs each can be more efficient than having a single data stream using the 8 SPEs. 1