Real-time servers have been widely explored in the scheduling literature to predictably execute aperiodic activities, as well as to allow hierarchical scheduling settings. As they facilitate timing isolation between different software components, there is a renewed interest for the adoption of fixed priority real-time servers in the automotive domain, as a way to implement more efficient reservation mechanisms than TDMA-based methods. In this paper, we focus on the Sporadic Server, which is the only fixed priority server supported by the POSIX standard. Despite its popularity, we realized that only sufficient schedulability conditions exist for real-time systems scheduled with a Sporadic Server. Thus, we develop a formal characterization of an exact response time analysis for fixed priority systems based on Sporadic Servers in a multi-level scheduling setting under preemptive scheduling. We then provide an experimental characterization of the schedulabilty improvement that can be obtained with respect to existing sufficient schedulability tests, proving the effectiveness of the proposed exact analysis.

在调度文献中已经广泛探索了实时服务器，以可预测地执行非周期性活动，并允许进行分层调度设置。由于它们促进了不同软件组件之间的时序隔离，因此人们重新关注在汽车领域采用固定优先级实时服务器，以实现比基于TDMA的方法更有效的预留机制。在本文中，我们重点介绍Sporadic服务器，这是POSIX标准唯一支持的固定优先级服务器。尽管它非常流行，但我们意识到对于使用Sporadic Server进行调度的实时系统，仅存在足够的可调度性条件。从而，我们基于抢先式调度的多层调度设置中的零散服务器为固定优先级系统开发了精确响应时间分析的形式化描述。然后，我们提供了针对可调度性改进的实验表征，可以相对于现有的足够的可调度性测试获得该性能，证明了所提出的精确分析的有效性。