Utilization-Based Scheduling of Flexible Mixed-Criticality Real-Time Tasks

TL;DR

This paper introduces a flexible mixed-criticality model for real-time systems that allows only the overrunning task to exhibit high-criticality behavior, improving resource efficiency and enabling dynamic service level adjustments.

Contribution

The paper proposes the FMC model that addresses impractical assumptions in traditional models, allowing more realistic task behavior and dynamic service level tuning under EDF-VD scheduling.

Findings

FMC model improves resource utilization over traditional models.

The schedulability analysis enables dynamic service level adjustment.

Experimental results show FMC's effectiveness compared to existing techniques.

Abstract

Mixed-criticality models are an emerging paradigm for the design of real-time systems because of their significantly improved resource efficiency. However, formal mixed-criticality models have traditionally been characterized by two impractical assumptions: once \textit{any} high-criticality task overruns, \textit{all} low-criticality tasks are suspended and \textit{all other} high-criticality tasks are assumed to exhibit high-criticality behaviors at the same time. In this paper, we propose a more realistic mixed-criticality model, called the flexible mixed-criticality (FMC) model, in which these two issues are addressed in a combined manner. In this new model, only the overrun task itself is assumed to exhibit high-criticality behavior, while other high-criticality tasks remain in the same mode as before. The guaranteed service levels of low-criticality tasks are gracefully degraded with the overruns of high-criticality tasks. We derive a utilization-based technique to analyze the schedulability of this new mixed-criticality model under EDF-VD scheduling. During runtime, the proposed test condition serves an important criterion for dynamic service level tuning, by means of which the maximum available execution budget for low-criticality tasks can be directly determined with minimal overhead while guaranteeing mixed-criticality schedulability. Experiments demonstrate the effectiveness of the FMC scheme compared with state-of-the-art techniques.