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1. Optimal soft real-time semi-partitioned scheduling made simple (and dynamic)

   https://doi.org/10.1145/3356401.3356402  

   Hobbs, Clara; Tong, Zelin; Anderson, James H. (November 2019, Proceedings of the 27th International Conference on Real-Time Networks and Systems)

   Semi-partitioned scheduling is an approach to multiprocessor real-time scheduling where most tasks are fixed to processors, while a small subset of tasks is allowed to migrate. This approach offers reduced overhead compared to global scheduling, and can reduce processor capacity loss compared to partitioned scheduling. Prior work has resulted in a number of semi-partitioned scheduling algorithms, but their correctness typically hinges on a complex intertwining of offline task assignment and online execution. This brittleness has resulted in few proposed semi-partitioned scheduling algorithms that support dynamic task systems, where tasks may join or leave the system at runtime, and few that are optimal in any sense. This paper introduces EDF-sc, the first semi-partitioned scheduling algorithm that is optimal for scheduling (static) soft real-time (SRT) sporadic task systems and allows tasks to dynamically join and leave. The SRT notion of optimality provided by EDF-sc requires deadline tardiness to be bounded for any task system that does not cause over-utilization. In the event that all tasks can be assigned as fixed, EDF-sc behaves exactly as partitioned EDF. Heuristics are provided that give EDF-sc the novel ability to stabilize the workload to approach the partitioned case as tasks join and leave the system. 

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2. Reducing Response-Time Bounds via Global Fixed Preemption Point EDF-like Scheduling

   Goh, Joseph; Anderson, J. H. (August 2023, Proceedings of the 29th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications)

   The fixed preemption point (FPP) model has been studied as an alternative to fully preemptive and non-preemptive models, as restricting preemptions to specific, predictable locations within a task’s execution can simplify overhead analysis without disallowing preemptions entirely. Prior work has produced response-time analyses for global Earliest Deadline First (G-EDF) scheduling under the FPP model. However, scheduling decisions based solely on task deadlines may be too coarsegrained and may not lead to the lowest response times. In this paper, we propose global FPP EDF-like (G-FPP-EL) scheduling, which assigns a priority point in time for each non-preemptive region of a task. We adapt compliant-vector analysis (CVA) to our model and present general response-time bounds for G-FPPEL schedulers. We then demonstrate that it is possible to design G-FPP-EL schedulers acheiving response-time bounds optimal under CVA and argue that such schedulers should replace global FPP EDF. 

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3. NPM-BUNDLE: Non-Preemptive Multitask Scheduling for Jobs with BUNDLE-Based Thread-Level Scheduling

   https://doi.org/10.4230/LIPIcs.ECRTS.2019.15  

   Tessler, Corey; Fisher, Nathan (July 2019, Leibniz international proceedings in informatics)

   The BUNDLE and BUNDLEP scheduling algorithms are cache-cognizant thread-level scheduling algorithms and associated worst case execution time and cache overhead (WCETO) techniques for hard real-time multi-threaded tasks. The BUNDLE-based approaches utilize the inter-thread cache benefit to reduce WCETO values for jobs. Currently, the BUNDLE-based approaches are limited to scheduling a single task. This work aims to expand the applicability of BUNDLE-based scheduling to multiple task multi-threaded task sets. BUNDLE-based scheduling leverages knowledge of potential cache conflicts to selectively preempt one thread in favor of another from the same job. This thread-level preemption is a requirement for the run-time behavior and WCETO calculation to receive the benefit of BUNDLE-based approaches. This work proposes scheduling BUNDLE-based jobs non-preemptively according to the earliest deadline first (EDF) policy. Jobs are forbidden from preempting one another, while threads within a job are allowed to preempt other threads. An accompanying schedulability test is provided, named Threads Per Job (TPJ). TPJ is a novel schedulability test, input is a task set specification which may be transformed (under certain restrictions); dividing threads among tasks in an effort to find a feasible task set. Enhanced by the flexibility to transform task sets and taking advantage of the inter-thread cache benefit, the evaluation shows TPJ scheduling task sets fully preemptive EDF cannot. 

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4. A Soft-Real-Time-Optimal Semi-Clustered Scheduler with a Constant Tardiness Bound

   https://doi.org/10.1109/RTCSA50079.2020.9203605  

   Ahmed, Shareef; Anderson, James H. (August 2020, Proceedings of the 26th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications)

   null (Ed.)

   Different global and semi-partitioned schedulers have been proposed that are soft-real-time (SRT) optimal for sporadic task systems, meaning they can guarantee bounded deadline tardiness. However, under known analyses, tardiness bounds increase with respect to the number of processors, which reduces the applicability of these schedulers in systems with a large number of processors. In this paper, a semi-clustered scheduler, SC-EDF, is presented that has a constant tardiness bound. SC-EDF partitions tasks into clusters, each of which may include one fractional processor. Each cluster is scheduled by G-EDF, and the fractional processors are realized using Pfair scheduling techniques. 

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5. Soft Real-Time Gang Scheduling

   Ahmed, Shareef; Anderson, James H. (December 2023, Proceedings of the 44th IEEE Real-Time Systems Symposium)

   Due to the emergence of parallel architectures and parallel programming frameworks, modern real-time applications are often composed of parallel tasks that can occupy multiple processors at the same time. Among parallel task models, gang scheduling has received much attention in recent years due to its performance efficiency and applicability to parallel architectures such as graphics processing units. Despite this attention, the soft real-time (SRT) scheduling of gang tasks has received little attention. This paper, for the first time, considers the SRT-feasibility problem for gang tasks. Necessary and sufficient feasibility conditions are presented that relate the SRTfeasibility problem to the HRT-feasibility problem of “equivalent” task systems. Based on these conditions, intractability results for SRT gang scheduling are derived. This paper also presents server-based scheduling policies, corresponding schedulability tests, and an improved schedulability condition for the global-earlies-tdeadline-first (GEDF) scheduling of gang tasks. Moreover, GEDF is shown to be non-optimal in scheduling SRT gang tasks. 

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