Towards completely fair scheduling on asymmetric single-ISA multicore processors.

Single-ISA asymmetric multicore processors (AMPs), which combine high-performance big cores with low-power small cores, were shown to deliver higher performance per watt than symmetric CMPs (Chip Multi-Processors). Previous work has highlighted that this potential of AMP systems can be realizable via OS scheduling. To date, most existing scheduling schemes for AMPs have been designed to optimize the system throughput, but they are inherently unfair. Although fairness-aware schedulers have been also proposed, they fail to effectively deal with user priorities and do not always ensure that equal-priority applications experience a similar slowdown. To overcome these limitations, we propose ACFS, an asymmetry-aware completely fair scheduler that seeks to optimize fairness while ensuring acceptable throughput. Our evaluation on real AMP hardware and using scheduler implementations in the Linux kernel demonstrates that ACFS achieves an average 23% fairness improvement over two state-of-the-art schemes, while providing higher system throughput. Throughput and fairness are largely conflicting optimization goals on AMPs.Previous asymmetry-aware schedulers fail to effectively deal with user priorities.ACFS achieves an average 23% fairness improvement over state-of-the-art schemes.Predicting cross-core performance on current AMPs is one of the major challenges.