Ya-Shu Chen

Online Real-Time Task Scheduling in Heterogeneous Multicore System-on-a-Chip

Online task scheduling in heterogeneous multicore system-on-a-chip is a challenging problem due to precedence constraints and nonpreemptive task execution in the synergistic processor core. This study first proposes an online heterogeneous dual-core scheduling framework for dynamic workloads with real-time constraints. The general purpose processor core and the synergistic processor core are dedicated to separate schedulers with different scheduling policies, and precedence constraints among tasks are dealt with through interaction between the two schedulers. This framework is also configurable for low priority inversion and high system utilization. We then extend this framework to heterogeneous multicore systems with well-known dispatcher schemas. This paper presents a real case study to show the practicability of the proposed methodology, and presents a series of extensive simulations to obtain comparison studies using different workloads and scheduling algorithms.

Energy-Efficient Task Synchronization for Real-Time Systems

In the past decade, energy-efficient real-time task scheduling has been widely explored in the form of various optimization problems. This paper considers energy-efficient real-time task synchronization protocols and the overhead of frequency switching in real systems design. We propose the concept of frequency locking to better manage the cost in frequency switching. To minimize the energy consumption and meet the timing constraints, algorithms are presented to assign tasks base frequencies under existing synchronization protocols which are then extended with the frequency locking concept. Finally, a series of extensive simulations is performed and a real case study is presented to evaluate the proposed methodology and obtain comparison studies using different workloads and protocols.

Data-locality-aware mapreduce real-time scheduling framework

A framework to manage interactive MapReduce applications with deadline constraint.A dispatcher to assign jobs to resources considering blocking and data-locality.A dynamic power management for MapReduce tasks to improve run-time energy efficiency.A schedulability test to ensure that all MapReduce tasks meet the timing constraints. MapReduce is widely used in cloud applications for large-scale data processing. The increasing number of interactive cloud applications has led to an increasing need for MapReduce real-time scheduling. Most MapReduce applications are data-oriented and nonpreemptively executed. Therefore, the problem of MapReduce real-time scheduling is complicated because of the trade-off between run-time blocking for nonpreemptive execution and data-locality. This paper proposes a data-locality-aware MapReduce real-time scheduling framework for guaranteeing quality of service for interactive MapReduce applications. A scheduler and dispatcher that can be used for scheduling two-phase MapReduce jobs and for assigning jobs to computing resources are presented, and the dispatcher enable the consideration of blocking and data-locality. Furthermore, dynamic power management for run-time energy saving is discussed. Finally, the proposed methodology is evaluated by considering synthetic workloads, and a comparative study of different scheduling algorithms is conducted.

Dynamic Task Scheduling and Processing Element Allocation for Multi-Function SoCs

This work is motivated by the rapid increasing of the design complexity of many embedded systems. It aims at the proposing of solutions to resolve the hardware contention issues of non-preemptive processing elements shared among tasks and the cost optimization. A software solution based on the starting time management is proposed to interleave task executions on processing elements. Algorithms are proposed to determine the required processing elements of selected types, when there is no knowledge on the releasing time of any task: When task release orders are known a priori, an optimal algorithm is presented if processing elements have the same cost; otherwise, a pseudo-polynomial-time algorithm based on dynamic programming is presented for optimal solutions. The performance of the algorithms is also evaluated for general cases

Real-time task scheduling anomaly: observations and prevention

This research is motivated by the practical needs in the porting of embedded software over platforms and the well-known multiprocessor anomaly [2, 3]. In particular, we consider the task scheduling problem when the system configuration changes. We show that new violations of the timing constraints of tasks might occur even when a more powerful processor or device is adopted. The concept of scheduler stability and rules are then proposed to prevent scheduling anomaly from happening for task executions that might be involved with task synchronization or I/O access. Finally, we explore policies in bounding the the duration time of scheduling anomaly.

An anomaly prevention approach for real-time task scheduling

This research responds to practical requirements in the porting of embedded software over platforms and the well-known multiprocessor anomaly. In particular, we consider the task scheduling problem when the system configuration changes. With mutual-exclusive resource accessing, we show that new violations of the timing constraints of tasks might occur even when a more powerful processor or device is adopted. The concept of scheduler stability and rules are then proposed to prevent scheduling anomaly from occurring in task executions that might be involved with task synchronization or I/O access. Finally, we explore policies for bounding the duration of scheduling anomalies.

FL-PCP: Frequency Locking for Energy-Efficient Real-Time Task Synchronization

In the past decade, energy-efficient real-time task scheduling has been widely explored in terms of various optimization problems. With a very different goal, this paper considers real-time task synchronization protocols with the minimization of energy consumption. We propose the concept of frequency locking and extend the priority ceiling protocol by locking the processor frequency in a restricted way so that the cost in frequency switching is better managed. Algorithms are proposed to assign tasks base frequencies in the minimization of the energy consumption and with the consideration of schedulability tests. The capability of the proposed methodology is evaluated by a series of experiments, for which encouraging results were presented.

Thermal-aware real-time task scheduling for three-dimensional multicore chip

Thermal management is a major design challenge in three-dimensional multicore chips. The process is complex because of the heat effect of vertically stacked cores and the difficulty of balancing performance requirements and overheating. This study proposes a thermal-aware real-time scheduling framework for three-dimensional (3D) multicore chips. The power-aware task partition and stack supervisor schemes help resolve the thermal stress produced by multiple vertically stacked cores. The proposed framework provides a quality of service guarantee under thermal constraints, and simultaneously, ensures optimal system performance. The results of a series of extensive simulations that the proposed method effectively prevents overheating without violating the quality of service guarantee.

Multi-layer bus minimization for SoC

The deployment of multiple processing elements such as a microprocessor or a Digital Signal Processor in embedded systems often results in significant communication overheads. The challenge lies in resolving the communication cost minimization problem, while simultaneously satisfying the timing constraints of job executions. In this paper, we explore bus-layer minimization problems by first identifying factors that contribute to the NP-hardness of these problems. Existing proposed algorithms and NP-hard problems are then identified and elucidated. A simulated annealing algorithm is proposed and compared with heuristics-based algorithms to provide further insights for system designers. Lastly, a series of extensive simulations is carried out and a case study is presented to show comparisons among different approaches and workloads.

A real-time configurable synchronization protocol for self-suspending process sets

While several of researchers have proposed excellent protocols on resource synchronization, little work has been done for processes that might suspend themselves for I/O access, especially when they tend to be more tolerant to multiple priority inversions. This paper presents research results extended from the concept of priority ceilings with the objective of satisfying different priority-inversion requirements for different processes. We aim at practical considerations in which processes might voluntarily give up CPU and be willing to receive more blocking time than those in more traditional approaches. Extensions on the proposed scheduling protocols for deadlock prevention are also considered.