Fine-Grained QoS Control via Tightly-Coupled Bandwidth Monitoring and Regulation for FPGA-Based Heterogeneous SoCs

Commercial embedded systems increasingly rely on heterogeneous architectures that integrate general-purpose, multi-core processors, and various hardware accelerators on the same chip. This provides the high performance required by modern applications at a low cost and low power consumption, but at the same time poses new challenges. Hardware resource sharing at various levels, and in particular at the main memory controller level, results in slower execution time for the application tasks, ultimately making the system unpredictable from the point of view of timing. To enable the adoption of heterogeneous systems-on-chip (System on Chips (SoCs)) in the domain of timing-critical applications several hardware and software approaches have been proposed, bandwidth regulation based on monitoring and throttling being one of the most widely adopted. Existing solutions, however, are either too coarse-grained, limiting the control over computing engines activities, or strongly platform-dependent, addressing the problem only for specific SoCs. This article proposes an innovative approach that can accurately control main memory bandwidth usage in FPGA-based heterogeneous SoCs. In particular, it controls system bandwidth by connecting a runtime bandwidth regulation component to FPGA-based accelerators. Our solution offers dynamically configurable, fine-grained bandwidth regulation – to adapt to the varying requirements of the application over time – at a very low overhead. Furthermore, it is entirely platform-independent, capable of integration with any FPGA-based accelerator. Developed at the register-transfer level using a reference SoC platform, it is designed for easy compatibility with any FPGA-based SoC. Experimental results conducted on the Xilinx Zynq UltraScale+ platform demonstrate that our approach (i) is more than $100\times$ faster than loosely-coupled, software controlled regulators; (ii) is capable of exploiting the system bandwidth 28.7% more efficiently than tightly-coupled hardware regulators (e.g., ARM CoreLink QoS-400, where available); (iii) enables task co-scheduling solutions not feasible with state-of-the-art bandwidth regulation methods.