Constrained Data-Age with Job-Level Dependencies: How to Reconcile Tight Bounds and Overheads

• Main Authors: Klaus, Tobias, Becker, Matthias, Schroder-Preikschat, Wolfgang, Ulbrich, Peter
• Format: Conference Proceeding
• Language: English
• Subjects: Analytical models; Automotive Systems; Concurrent Engineering Paradigm; Data Age Constraints; End to End Latency; Job level Dependencies; Job shop scheduling; Logical Execution Time; Real Time Systems; Registers; Schedulability; Schedules; Semantics; Static Analysis; Synchronization; Upper bound
• ISSN: 2642-7346
• DOI: 10.1109/RTAS52030.2021.00014

Many industrial real-time systems rely on the implicit register communication paradigm to minimize overheads and ease distributed development. Here, tasks follow a simple input-processing-output scheme, and data is passed without synchronization by the last-is-best semantics. In these systems, the age of data is the primary real-time objective, which is defined by data-flow chains that span from the system's inputs to outputs. Consequently, a real-time analysis aims to provide guarantees on worst-case data age. In general, there are two main approaches: (1) Task-level scheduling such that inter-task communication is arranged at the beginning and end of a task's execution interval, which guarantees a deterministic yet highly pessimistic data age. (2) Job-level dependencies (JLD) that are added at critical points in the schedule to link specific job instances of tasks of a multi-rate data-flow chain, which provides tighter upper bounds on data ages. However, the drawback is that JLDs induce substantial synchronization overheads, impact the overall schedulability, and are much more challenging to implement. In this paper, we address the trade-off between tight data-age guarantees, synchronization overheads, and schedulability in multi-core settings. Our proposed solution is to combine the potential of job-level optimization with the determinism and low overheads of static, task-level approaches. Therefore, we present a novel execution model to efficiently map data-age constrained tasksets with job-level dependencies on event-triggered systems by automated system analysis and transformation. Experimental results of an extensive real-world case study substantiate that our approach can further tighten data-age bounds, reduce overheads, and ease schedulability.