SPAMeR: Speculative Push for Anticipated Message Requests in Multi-Core Systems

Abstract

With increasing core counts and multiple levels of cache memories, scaling multi-threaded and task-level parallel workloads is continuously becoming a challenge. A key challenge to scaling the number of communicating tasks (or threads) is the rate at which existing communication mechanisms scale (in terms of latency and bandwidth). Architectures with hardware accelerated queuing operations have the potential to reduce the latency and improve scalability of moving data between processing elements, reducing synchronization penalties, and thereby improving the performance of task-level parallel workloads. While hardware queues reduce synchronization penalties, they cannot fully hide load-to-use latency, i.e., perfect pipelines often are not realized. There is the potential, however, for better overlap. If the inter-processor communication latency is equal to or less than the time spent processing a message at the consumer, any and all latency may be overlapped while the consumer is processing. We exploit this property to speedup parallel applications above and beyond existing hardware queues. In this paper, we present SPAMeR, a speculation mechanism built on top of a state-of-the-art hardware-driven message queue architecture. SPAMeR has the capability to speculatively push messages in anticipation of consumer message requests. Unlike pre-fetch approaches which predict what addresses to fetch next, with a queue we know exactly what data is needed next but not when it is needed; SPAMeR adds algorithms that attempt to predict this. We evaluate the effectiveness of SPAMeR with a set of diverse task-parallel benchmarks utilizing the gem5 full system simulator, and observe a 1.33 × average speedup.