Delivering fairness on asymmetric multicore systems via contention-aware scheduling

Abstract

Asymmetric single-ISA multicore processors (AMPs), which integrate high-performance big cores and low-power small cores, were shown to deliver better energy efficiency than symmetric multicores for diverse workloads. Previous work has highlighted that this potential of AMP systems can be realizable with help from the OS scheduler. Notably, delivering fairness on AMPs still constitutes an important challenge, as it requires the scheduler to accurately track the progress of each thread as it runs on the various core types throughout the execution. In turn, this progress depends on the speedup that an application derives on a big core relative to a small one. While existing fairness-aware schedulers take application relative speedup into consideration when tracking progress, they do not cater to the performance degradation that may occur naturally due to contention on shared resources among cores, such as the last-level cache or the memory bus. In this paper, we propose CAMPS, a contention-aware fair scheduler for AMPs. Our experimental evaluation, which employs real asymmetric hardware and scheduler implementations in the Linux kernel, demonstrates that CAMPS improves fairness by 10.6% on average with respect to a state-of-the-art fairness-aware scheme, while delivering higher throughput.