Insik Shin

Hierarchical Scheduling Framework for Virtual Clustering of Multiprocessors

Scheduling of sporadic task systems on multiprocessor platforms is an area which has received much attention in the recent past. It is widely believed that finding an optimal scheduler is hard, and therefore most studies have focused on developing algorithms with good utilization bounds. These algorithms can be broadly classified into two categories: partitioned scheduling in which tasks are statically assigned to individual processors, and globalscheduling in which each task is allowed to execute on any processor in the platform. In this paper we consider a third, more general, approach called cluster-based scheduling. In this approach each task is statically assigned to a processor cluster, tasks in each cluster areglobally scheduled among themselves, and clusters in turn are scheduled on the multiprocessor platform. We develop techniques to support such cluster-based scheduling algorithms, and also consider properties that minimize processor utilization of individual clusters. Since neither partitioned nor global strategies dominate over the other, cluster-based scheduling is a natural direction for research towards achieving improved utilization bounds.

SIRAP: a synchronization protocol for hierarchical resource sharingin real-time open systems

This paper presents a protocol for resource sharing in a hierarchical real-time scheduling framework. Targeting real-time open systems, the protocol and the scheduling framework significantly reduce the efforts and errors associated with integrating multiple semi-independent subsystems on a single processor. Thus, our proposed techniques facilitate modern software development processes, where subsystems are developed by independent teams (or subcontractors) and at a later stage integrated into a single product. Using our solution, a subsystem need not know, and is not dependent on, the timing behaviour of other subsystems; even though they share mutually exclusive resources. In this paper we also prove the correctness of our approach and evaluate its efficiency.

Mixed-criticality scheduling on multiprocessors

The scheduling of mixed-criticality implicit-deadline sporadic task systems on identical multiprocessor platforms is considered. Two approaches, one for global and another for partitioned scheduling, are described. Theoretical analyses and simulation experiments are used to compare the global and partitioned scheduling approaches.

Optimal virtual cluster-based multiprocessor scheduling

Scheduling of constrained deadline sporadic task systems on multiprocessor platforms is an area which has received much attention in the recent past. It is widely believed that finding an optimal scheduler is hard, and therefore most studies have focused on developing algorithms with good processor utilization bounds. These algorithms can be broadly classified into two categories: partitioned scheduling in which tasks are statically assigned to individual processors, and global scheduling in which each task is allowed to execute on any processor in the platform. In this paper we consider a third, more general, approach called cluster-based scheduling. In this approach each task is statically assigned to a processor cluster, tasks in each cluster are globally scheduled among themselves, and clusters in turn are scheduled on the multiprocessor platform. We develop techniques to support such cluster-based scheduling algorithms, and also consider properties that minimize total processor utilization of individual clusters. In the last part of this paper, we develop new virtual cluster-based scheduling algorithms. For implicit deadline sporadic task systems, we develop an optimal scheduling algorithm that is neither Pfair nor ERfair. We also show that the processor utilization bound of us-edf{m/(2m−1)} can be improved by using virtual clustering. Since neither partitioned nor global strategies dominate over the other, cluster-based scheduling is a natural direction for research towards achieving improved processor utilization bounds.

Global EDF Schedulability Analysis for Synchronous Parallel Tasks on Multicore Platforms

The trend towards multi-core/many-core architectures is well underway. It is therefore becoming very important to develop software in ways that take advantage of such parallel architectures. This particularly entails a shift in programming paradigms towards fine-grained, thread-parallel computing. Many parallel programming models have been introduced targeting such intra-task thread-level parallelism. However, most successful results on traditional multi-core real-time scheduling are focused on sequential programming models. For example, thread-level parallelism is not properly captured into the concept of interference, which is key to many schedulability analysis techniques. Thereby, most interference-based analysis techniques are not directly applicable to parallel programming models. Motivated by this, we extend the notion of interference to capture thread-level parallelism more accurately. We then leverage the proposed notion of parallelism-aware interference to derive efficient EDF schedulability tests that are directly applicable to synchronous parallel task models on multi-core platforms. Our evaluation results indicate that the proposed analysis significantly advances the state-of-the-art in EDF schedulability analysis for synchronous parallel tasks.

Overrun Methods and Resource Holding Times for Hierarchical Scheduling of Semi-Independent Real-Time Systems

The hierarchical scheduling framework (HSF) has been introduced as a design-time framework to enable compositional schedulability analysis of embedded software systems with real-time properties. In this paper, a software system consists of a number of semi-independent components called subsystems. Subsystems are developed independently and later integrated to form a system. To support this design process, in the paper, the proposed methods allow non-intrusive configuration and tuning of subsystem timing-behavior via subsystem interfaces for selecting scheduling parameters. This paper considers three methods to handle overruns due to resource sharing between subsystems in the HSF. For each one of these three overrun methods corresponding scheduling algorithms and associated schedulability analysis are presented together with analysis that shows under what circumstances one or the other is preferred. The analysis is generalized to allow for both fixed priority scheduling (FPS) and earliest deadline first (EDF) scheduling. Also, a further contribution of the paper is the technique of calculating resource-holding times within the framework under different scheduling algorithms; the resource holding times being an important parameter in the global schedulability analysis.

Synthesis of Optimal Interfaces for Hierarchical Scheduling with Resources

This paper presents algorithms that (1) facilitate system-independent synthesis of timing-interfaces for subsystems and (2) system-level selection of interfaces to minimize CPU load. The results presented are developed for hierarchical fixed-priority scheduling of subsystems that may share logical recourses (i.e. semaphores). We show that the use of shared resources results in a tradeoff problem, where resource locking times can be traded for CPU allocation, complicating the problem of finding the optimal interface configuration subject to schedulability. This paper presents a methodology where such a tradeoff can be effectively explored. It first synthesizes a bounded set of interface-candidates for each subsystem, independently of the final system, such that the set contains the interface that minimizes system load for any given system. Then, integrating subsystems into a system, it finds the optimal selection of interfaces. Our algorithms have linear complexity to the number of tasks involved. Thus, our approach is also suitable for adaptable and reconfigurable systems.

A Synchronization Protocol for Temporal Isolation of Software Components in Vehicular Systems

We present a method that allows for integration of individually developed functions of software components into a predictable real-time system. The method has been designed to provide a lightweight mechanism that gives temporal firewalls between functions, preventing unpredictable side effects during function integration. The method maps well to the AUTOSAR (automotive open system architecture) software component model and can thus be used to facilitate seamless and predictable integration and isolation of AUTOSAR components that have been developed by different manufacturers. Specifically, this paper presents a protocol for synchronization in a hierarchical real-time scheduling framework. Using our protocol, a software component does not need to know, and is not dependent on, the timing behavior of software components belonging to other functions; even though they share mutually exclusive resources. In this paper, we also prove the correctness of our approach and evaluate its efficiency and cost in terms of system load in a vehicular context.

GreenBag: Energy-Efficient Bandwidth Aggregation for Real-Time Streaming in Heterogeneous Mobile Wireless Networks

Modern mobile devices are equipped with multiple network interfaces, including 3G/LTE and WiFi. Bandwidth aggregation over LTE and WiFi links offers an attractive opportunity of supporting bandwidth-intensive services, such as high-quality video streaming, on mobile devices. However, achieving effective bandwidth aggregation in mobile environments raises several challenges related to deployment, link heterogeneity, network fluctuation, and energy consumption. We present GreenBag, an energy-efficient bandwidth aggregation middleware that supports real-time data-streaming services over asymmetric wireless links, requiring no modifications to the existing Internet infrastructure and servers. GreenBag employs several techniques, including medium load balancing, efficient segment management, and energy-aware mode control, to resolve such challenges. We implement a prototype of GreenBag on Android-based mobile devices which hosts, to the best knowledge of the authors, the first LTE-enabled bandwidth aggregation prototype for energy-efficient real-time video streaming. Our experiment results in both emulated and real-world environments show that GreenBag not only achieves good bandwidth aggregation to provide QoS in bandwidth-scarce environments but also efficiently saves energy on mobile devices. Moreover, energy-aware GreenBag can minimize video interruption while consuming 14-25% less energy than the non-energy-aware counterpart in real-world experiments.

SymPhoney: a coordinated sensing flow execution engine for concurrent mobile sensing applications

Emerging mobile sensing applications are changing the characteristics of smartphone workloads. Whereas typical mobile applications run alone in the foreground interacting with users, sensing applications concurrently run in the background, providing unobtrusive monitoring services. Such concurrent sensing workloads raise a new challenge incurring severe resource contention among themselves and with other foreground applications. To address the challenge, we develop SymPhoney, a coordinated sensing flow execution engine to support concurrent sensing applications. As its key approach, we develop a novel sensing-flow-aware coordination. We first introduce the new concept of frame externalization i.e., to identify and externalize semantic structures embedded in otherwise flat sensing data streams. Leveraging the identified frame structures, SymPhoney develops frame-based coordination and scheduling mechanisms, which effectively coordinates the resource use of concurrent contending applications and maximize their utilities even under severe resource contention. We implemented several sensing applications on top of the SymPhoney engine and performed extensive experiments, showing effective coordination capability of SymPhoney.