Rapid Development of OS Support with PMCSched for Scheduling on Asymmetric Multicore Systems

Abstract

Asymmetric multicore processors (AMPs) couple high-performance big cores and power-efficient small ones, all exposing a shared instruction set architecture to software, but with different microarchitectural features. The energy efficiency benefits of AMPs together with the general-purpose nature of the various cores, have led hardware manufactures to build commercial AMP-based products, first for the mobile and embedded domains, and more recently for the desktop market segment, as with the Intel Alder Lake processor family. This indicates that AMPs may become a solid and more energy efficient replacement to symmetric multicores in a wide range of application domains.

Previous research has demonstrated that the system software can substantially improve scheduling –critical to get the most out of heterogeneous cores– by leveraging hardware facilities that are directly managed by the OS, such as performance monitoring counters, or the recently introduced Intel Thread Director technology. Unfortunately, the OS-level support enabling to access scheduling-relevant hardware support may take a long time to be adopted in operating systems, or may come in forms that make its utilization challenging from specific levels of the system software stack, especially in production systems. To fill this gap, we propose the PMCSched framework, which enables the creation of custom OS support on Linux to aid in the design of novel scheduling and resource-management policies for multicores implemented at different layers of the system software, but without requiring to patch the kernel. To demonstrate the potential of our framework, we implement a set of OS-level schedulers for AMPs, that make use of custom OS extensions to access scheduling-relevant hardware facilities in an x86 AMP processor.