MemPol: Policing Core Memory Bandwidth from Outside of the Cores

Abstract

In today’s multiprocessor systems-on-a-chip (MP- SoC), the shared memory subsystem is a known source of temporal interference. The problem causes logically independent cores to affect each other’s performance, leading to pessimistic worstcase execution time (WCET) analysis. One of the most practical techniques to mitigate interference is memory regulation via throttling. Traditional regulation schemes rely on a combination of timer and performance counter interrupts to be delivered and processed on the same cores running real-time workload. Unfortunately, to prevent excessive overhead, regulation can only be enforced at a millisecond-scale granularity. In this work, we present a novel regulation mechanism from outside the cores that monitors performance counters for the application core’s activity in main memory at a microsecond scale. The approach is fully transparent to the applications on the cores, and can be implemented using widely available onchip debug facilities. The presented mechanism also allows more complex composition of metrics to enact load-aware regulation. For instance, it allows redistributing unused bandwidth between cores while keeping the overall memory bandwidth of all cores below a given threshold. We implement our approach on a host of embedded platforms and carry out an in-depth evaluation on the Xilinx Zynq UltraScale+ZCUl02 platform using the SD-VBS.