Dynamic C-Slow Pipelining for HLS

Abstract

In high-level synthesis (HLS), loop pipelining allows multiple iterations of a loop to be executed concurrently. The start time of the operations in each iteration can be determined either at compile time (static pipelining) or at run time (dynamic pipelining). There has been recent interest in dynamic pipelining, as it can overcome the conservatism of static analysis, potentially achieving better performance.In order to ensure correctness in the presence of memory dependences, existing state-of-the-art dynamic pipelining algorithms schedule control flow between basic blocks in the original program order even if they allow pipelining of data flow. This allows source code to be compiled compositionally, ‘stitching together’ the resulting hardware components to produce the final hardware design. However, this approach can result in suboptimal throughput.In this paper we propose a technique to statically determine a set of possible memory-legal control flows for nested loops, together with a scheduler component able to select from that set efficiently at run time, enabling dynamic execution of control as a C-slow pipeline. An empirical evaluation on a range of applications suggests that by using this approach, we can obtain 2.9× speedup with 7% area overhead compared to a dynamic scheduling approach with sequential control flow.