Efficient Control and Communication Paradigms for Coarse-Grained Spatial Architectures

Recently there has been interest in exploring the acceleration of non-vectorizable workloads with spatially-programmed architectures that are designed to efficiently exploit pipeline parallelism. Such an architecture faces two main problems: A) how to efficiently control each processing element (PE) in the system, and B) how to facilitate inter-PE communication without the overheads of traditional shared-memory coherent memory. In this paper, we explore solving these problems using triggered instructions, and latency- insensitive channels. Triggered instructions completely eliminate the program counter and allow programs to transition concisely between states without explicit branch instructions. Latency-insensitive channels allow efficient communication of inter-PE control information, while simultaneously enabling flexible code placement and improving tolerance for variable events such as cache accesses. Together, these approaches provide a unified mechanism to avoid over-serialized execution, essentially achieving the effect of techniques such as dynamic instruction reordering and multithreading.

Our analysis shows that a spatial accelerator using triggered instructions and latency-insensitive channels can achieve 8× greater area-normalized performance than a traditional general-purpose processor. Further analysis shows that triggered control reduces the number of static and dynamic instructions in the critical paths by 62% and 64% respectively over a program-counter style baseline, increasing the performance of the spatial programming approach by 2.0×.