Massively Parallel Server Processors

Modern data centers enjoy massive degrees of request-level parallelism with significant cross-request similarity. Although similar requests follow similar instruction sequences, conventional processors service them individually and do not take full advantage of cross-request similarity. Single-Instruction Multiple-Thread (SIMT) architectures can leverage this similarity, however, existing SIMT processors-chief among them, GPUs-are ill-suited for server applications, as they are specifically designed to maximize throughput at the expense of latency, preventing them from meeting server QoS requirements. We advocate a new approach to SIMT server processors, namely Massively Parallel Server Processors (MPSPs), which we outline in this paper. To begin to understand their architectural needs, we measure the degree of control-flow and memory-access divergence encountered when running unmodified server applications on MPSP-style processors. Our preliminary results indicate that a software scheduler that bundles together similar requests can minimize control-flow divergence, making SIMT execution of unmodified server code feasible. Moreover, we find that memory-access divergence, although significant in raw numbers, can be tackled with changes in stack and heap layouts. Overall, our results encourage further consideration of MPSPs as a promising architecture for server processors.