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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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RT-Gang: Real-Time Gang Scheduling Framework for Safety-Critical Systems
In this paper, we present RT-Gang: a novel realtime gang scheduling framework that enforces a one-gang-at-atime policy. We find that, in a multicore platform, co-scheduling multiple parallel real-time tasks would require highly pessimistic worst-case execution time (WCET) and schedulability analysis—even when there are enough cores—due to contention in shared hardware resources such as cache and DRAM controller. In RT-Gang, all threads of a parallel real-time task form a real-time gang and the scheduler globally enforces the one-gangat-a-time scheduling policy to guarantee tight and accurate task WCET. To minimize under-utilization, we integrate a state-of-the-art memory bandwidth throttling framework to allow safe execution of best-effort tasks. Specifically, any idle cores, if exist, are used to schedule best-effort tasks but their maximum memory bandwidth usages are strictly throttled to tightly bound interference to real-time gang tasks. We implement RT-Gang in the Linux kernel and evaluate it on two representative embedded multicore platforms using both synthetic and real-world DNN workloads. The results show that RT-Gang dramatically improves system predictability and the overhead is negligible.
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- Award ID(s):
- 1815959
- PAR ID:
- 10097576
- Date Published:
- Journal Name:
- Proceedings - IEEE Real-Time and Embedded Technology and Applications Symposium
- ISSN:
- 1545-3421
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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