SOCIAL SCIENCES POSTGRADUATE INTERNATIONAL SEMINAR (SSPIS) 2017

The objectives of this seminar are: To provide an avenue for postgraduate students to present their research findings, impart knowledge and get feedback; To promote interactions among participants; To enhance networking among researchers; and To assist postgraduate students with publication opportunities

Period and Computational Elasticity for Adaptive Real-Time Systems

A wide range range of real-world applications (including multimedia players, ad-hoc communication networks, online trading, radar tracking software, and other adaptive control algorithms) need adaptive adjustment to their resource utilizations at run-time, while still maintaining real-time guarantees. The elastic task model of soft real-time systems allows for the run-time manipulation of tasks’ processor utilizations in order to maintain a system-wide quality of service or accommodate needs of other tasks by assigning each task a period within a specified range. As originally presented, only sequential tasks executing on a single processor were considered. However, in the two decades since the elastic task model was first introduced, multiprocessor systems have become increasingly prevalent. This dissertation appropriately extends the elastic task model to include both multiprocessor scheduling of sequential adaptive tasks and scheduling of adaptive tasks with internal parallelism. It also introduces novel elastic concepts in which 1) tasks can vary their computational loads rather than their periods and 2) the more realistic scenario in which tasks are allowed to adapt among a discrete set of candidate processor utilizations rather than over a continuous range. A runtime system for parallel elastic tasks is also presented and used to demonstrate the benefit of discrete elastic scheduling by enabling adaptation in the application domain of real-time hybrid simulation (RTHS)

Multi-core devices for safety-critical systems: a survey

Multi-core devices are envisioned to support the development of next-generation safety-critical systems, enabling the on-chip integration of functions of different criticality. This integration provides multiple system-level potential benefits such as cost, size, power, and weight reduction. However, safety certification becomes a challenge and several fundamental safety technical requirements must be addressed, such as temporal and spatial independence, reliability, and diagnostic coverage. This survey provides a categorization and overview at different device abstraction levels (nanoscale, component, and device) of selected key research contributions that support the compliance with these fundamental safety requirements.This work has been partially supported by the Spanish Ministry of Economy and Competitiveness under grant TIN2015-65316-P, Basque Government under grant KK-2019-00035 and the HiPEAC Network of Excellence. The Spanish Ministry of Economy and Competitiveness has also partially supported Jaume Abella under Ramon y Cajal postdoctoral fellowship (RYC-2013-14717).Peer ReviewedPostprint (author's final draft

Cache Related Pre-emption Delays in Embedded Real-Time Systems

Real-time systems are subject to stringent deadlines which make their temporal behaviour just as important as their functional behaviour. In multi-tasking real-time systems, the execution time of each task must be determined, and then combined together with information about the scheduling policy to ensure that there are enough resources to schedule all of the tasks. This is usually achieved by performing timing analysis on the individual tasks, and then schedulability analysis on the system as a whole. In systems with cache, multiple tasks can share this common resource which can lead to cache-related pre-emption delays (CRPD) being introduced. CRPD is the additional cost incurred from resuming a pre-empted task that no longer has the instructions or data it was using in cache, because the pre-empting task(s) evicted them from cache. It is therefore important to be able to account for CRPD when performing schedulability analysis. This thesis focuses on the effects of CRPD on a single processor system, further expanding our understanding of CRPD and ability to analyse and optimise for it. We present new CRPD analysis for Earliest Deadline First (EDF) scheduling that significantly outperforms existing analysis, and then perform the first comparison between Fixed Priority (FP) and EDF accounting for CRPD. In this comparison, we explore the effects of CRPD across a wide range of system and taskset parameters. We introduce a new task layout optimisation technique that maximises system schedulability via reduced CRPD. Finally, we extend CRPD analysis to hierarchical systems, allowing the effects of cache when scheduling multiple independent applications on a single processor to be analysed

Scheduling for Mixed-criticality Hypervisor Systems in the Automotive Domain

This thesis focuses on scheduling for hypervisor systems in the automotive domain. Current practices are primarily implementation-agnostic or are limited by lack of visibility during the execution of partitions. The tasks executed within the partitions are classified as event-triggered or time-triggered. A scheduling model is developed using a pair of a deferrable server and a periodic server per partition to provide low latency for event-triggered tasks and maximising utilisation. The developed approach enforces temporal isolation between partitions and ensures that time-triggered tasks do not suffer from starvation. The scheduling model was extended to support three criticality levels with two degraded modes. The first degraded mode provides the partitions with additional capacity by trading-off low latency of event-driven tasks with lower overheads and utilisation. Both models were evaluated by forming a case study using real ECU application code. A second case study was formed inspired from the Olympus Attitude and Orbital Control System (AOCS) to further evaluate the proposed mixed-criticality model. To conclude, the contributions of this thesis are addressed with respect to the research hypothesis and possible avenues for future work are identified