Design space exploration of hardware task superscalar architecture

Abstract

For current high performance computing systems, exploiting concurrency is a serious and important challenge. Recently, several dynamic software task management mechanisms have been proposed. In particular, task-based dataflow programming models which benefit from dataflow principles to improve task-level parallelism and overcome the limitations of static task management systems. However, these programming models rely on software-based dependency analysis, which are performed inherently slowly; and this limits their scalability specially when there is fine-grained task granularity and a large amount of tasks. Moreover, task scheduling in software introduces overheads, and so becomes increasingly inefficient with the number of cores. In contrast, a hardware scheduling solution, like Task SuperScalar (TSS), can achieve greater values of speed-up because a hardware task scheduler requires fewer cycles than the software version to dispatch a task. TSS combines the effectiveness of Out-of-Order processors together with the task abstraction. It has been implemented in software with limited parallelism and high memory consumption due to the nature of the software implementation. Hardware Task Superscalar (HTSS) is proposed to solve these drawbacks. HTSS is designed to be integrated in a future high performance computer with the ability to exploit fine-grained task parallelism. In this article, a deep latency and design space exploration of HTSS is described. For design space exploration, we have designed a full cycle-accurate simulator of HTSS, called SimTSS. The simulator has been tuned based on latency exploration of HTSS components resulted from VHDL description of each component. As the result of this exploration, we have found the number of components and memory capacity of HTSS for HPC systems.