Adrián Pousa

ACFS: a completely fair scheduler for asymmetric single-isa multicore systems

Single-ISA (instruction set architecture) asymmetric multicore processors (AMPs) were shown to deliver higher performance per watt and area than symmetric CMPs (Chip Multi-Processors) for applications with diverse architectural requirements. A large body of work has demonstrated that this potential of AMP systems can be realizable via OS scheduling. Yet, existing schedulers that seek to deliver fairness on AMPs do not ensure that equal-priority applications experience the same slowdown when sharing the system. Moreover, most of these schemes are also subject to high throughput degradation and fail to effectively deal with user priorities. In this work 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 on a general-purpose OS, demonstrates that ACFS achieves an average 11% fairness improvement over state-of-the-art schemes, while providing better system throughput.

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.

Exploring the Throughput-Fairness Trade-off on Asymmetric Multicore Systems

Symmetric-ISA (instruction set architecture) asymmetric-performance multicore processors (AMPs) were shown to deliver higher performance per watt and area than symmetric CMPs (Chip Multi-Processors). Previous work has shown that this potential of AMP systems can be realizable thanks to the OS scheduler. Existing scheduling schemes that deliver fairness and priority enforcement on AMPs do not cater to the fact that applications in a multiprogram workload may derive different benefit from using fast cores in the system. As a result, they are likely to perform thread-to-core mappings that degrade the system throughput. To address this limitation, we propose Prop-SP, a scheduling algorithm that aims to improve the throughput-fairness trade-off on AMPs. Our evaluation on real hardware, and using scheduler implementations on a general-purpose OS, reveals that Prop-SP delivers a better throughput-fairness trade-off than state-of-the-art schedulers for a wide variety of multi-application workloads.

PMCTrack: Delivering Performance Monitoring Counter Support to the OS Scheduler

Hardware performance monitoring counters (PMCs) have proven effective in characterizing application performance. Because PMCs can only be accessed directly at the OS privilege level, kernellevel tools must be developed to enable the end-user and userspace programs to access PMCs. A large body of work has demonstrated that the OS can perform effective runtime optimizations in multicore systems by leveraging performance-counter data. Special attention has been paid to optimizations in the OS scheduler. While existing performance monitoring tools greatly simplify the collection of PMC application data from userspace, they do not provide an architecture-agnostic kernel-level mechanism that is capable of exposing high-level PMC metrics to OS components, such as the scheduler. As a result, the implementation of PMC-based OS scheduling schemes is typically tied to specific processor models. To address this shortcoming we present PMCTrack, a novel tool for the Linux kernel that provides a simple architecture-independent mechanism that makes it possible for the OS scheduler to access per-thread PMC data. Despite being an OSoriented tool, PMCTrack still allows the gathering of monitoring data from userspace, enabling kernel developers to carry out the necessary offline analysis and debugging to assist them during the scheduler design process. In addition, the tool provides both the OS and the user-space PMCTrack components with other insightful metrics available in modern processors and which are not directly exposed as PMCs, such as cache occupancy or energy consumption. This information is also of great value when it comes to analyzing the potential benefits of novel scheduling policies on real systems. In this paper, we analyze different case studies that demonstrate the flexibility, simplicity and powerful features of PMCTrack.

On the Interplay Between Throughput, Fairness and Energy Efficiency on Asymmetric Multicore Processors

Asymmetric single-ISA multicore processors (AMPs), which integrate highperformance big cores and low-power small cores, were shown to deliver higher performance per watt than symmetric multicores. Previous work has highlighted that this potential of AMP systems can be realizable by scheduling the various applications in a workload on the most appropriate core type. A number of scheduling schemes have been proposed to accomplish different goals, such as system throughput optimization, enforcing fairness or reducing energy consumption. While the interrelationship between throughput and fairness on AMPs has been comprehensively studied, the impact that optimizing energy efficiency has on the other two aspects is still unclear. To fill this gap, we carry out a comprehensive analytical and experimental study that illustrates the interplay between throughput, fairness and energy efficiency on AMPs. Our analytical study allowed us to define the energy-efficiency factor (EEF) metric, which aids the OS scheduler in identifying which applications are more suitable for running on the various cores to ensure a good balance between performance and energy consumption. We propose two energy-aware OS-level schedulers that leverage the EEF metric; the first one strives to optimize the energy-delay product (EDP), the second scheduler can be configured to optimize different metrics on the AMP. To demonstrate the effectiveness of these proposals, we performed an extensive evaluation and comparison with state-of-the-art schemes by using real asymmetric hardware and scheduler implementations in the Linux kernel.

Experiences with Electronic Vote: Challenges and Solutions

This paper presents results of a research on electronic voting carried out by the Institute of Research in Computer Science LIDI of the School of Computer Science of the National University of La Plata, Argentina, as part of research in e-Government developed since 2003. In particular, the topic of electronic vote has generated various experiences that allowed developing different election models for public and private environments. These experiences have resulted in the transfer of technology to several sectors