Enhancing the real-time capabilities of the Linux kernel

Sousa, Paulo Baltarejo; Pereira, Nuno; Tovar, Eduardo

doi:10.1145/2452537.2452546

Cited by 6 publications

(8 citation statements)

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“…In the context of slot-based task-splitting scheduling algorithms, although some practical works (Sousa et al 2010(Sousa et al , 2011a(Sousa et al , 2012Bastoni et al 2011) have clearly demonstrated that these scheduling schemes are practical to implement in a real system, the practice also shows some performance degradation compared to what is theoretically achievable, due to various sources of overheads often unaccounted for by the theory. For instance, most theoretical works assume that task switching is instantaneous, but, in practice, it is time consuming because the operating system has to save the state of one task and restore that of another task.…”

Section: Contribution Of This Articlementioning

confidence: 99%

“…This new schedulability analysis supersedes all previous utilization-based analyses. Further, it defines new schedulability tests that incorporate all real-world overheads incurred by implementations of the S-EKG and NPS-F algorithms (Sousa et al , 2012.…”

Section: New Demand-based and Overhead-aware Schedulability Analysismentioning

confidence: 99%

“…In this subsection, we provide an overview of the overheads that may arise in an implementation of a slot-based task-× splitting scheduling algorithm. This overview is based on implementations (Sousa et al , 2012 of S-EKG and NPS-F in the Linux kernel for the 64 architecture.…”

Section: Overheadsmentioning

confidence: 99%

“…On slot-based task-splitting algorithms, a server's tasks share the processor with other tasks whose servers are assigned to the same processor. Consistent with implementation (Sousa et al , 2012 we assume that all jobs of a task are released on the processor(s) to which the task is assigned. As shown in Fig.…”

Section: Non-split Serversmentioning

confidence: 99%

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Unified overhead-aware schedulability analysis for slot-based task-splitting

et al. 2014

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Hard real-time multiprocessor scheduling has seen, in recent years, the flourishing of semi-partitioned scheduling algorithms. This category of scheduling schemes combines elements of partitioned and global scheduling for the purposes of achieving efficient utilization of the system's processing resources with strong schedulability guarantees and with low dispatching overheads. The sub-class of slot-based "tasksplitting" scheduling algorithms, in particular, offers very good trade-offs between schedulability guarantees (in the form of high utilization bounds) and the number of preemptions/migrations involved. However, so far there did not exist unified scheduling theory for such algorithms; each one was formulated in its own accompanying analysis. This article changes this fragmented landscape by formulating a more unified schedulability theory covering the two state-of-the-art slot-based semi-partitioned algorithms, S-EKG and NPS-F (both fixed job-priority based). This new theory is based on exact schedulability tests, thus also overcoming many sources of pessimism in existing analysis. In turn, since schedulability testing guides the task assignment under the schemes in consideration, we also formulate an improved task assignment procedure. As the other main contribution of this article, and as a response to the fact that many unrealistic assumptions, present in the original theory, tend to undermine the theoretical potential of such scheduling schemes, we identified and modelled into the new analysis all overheads incurred by the algorithms in consideration. The outcome is a new overhead-aware schedulability analysis that permits increased efficiency and reliability. The merits of this new theory are evaluated by an extensive set of experiments.

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Section: Contribution Of This Articlementioning

confidence: 99%

Section: New Demand-based and Overhead-aware Schedulability Analysismentioning

confidence: 99%

Section: Overheadsmentioning

confidence: 99%

Section: Non-split Serversmentioning

confidence: 99%

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Unified overhead-aware schedulability analysis for slot-based task-splitting

et al. 2014

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“…However, over the years, many of the improvements designed and developed by the PREEMPT_RT project (documentation is maintained on the Linux Foundation Wiki [1]) are now part of the mainline Linux kernel according to the Linutronix Co. [2]. In the past, approaches that have been considered in providing a Linux kernel with real-time capabilities, either improve the Linux kernel itself so that it provides bounded latencies for real-time applications (e.g., the PREEMPT_RT project) or add a layer below the Linux kernel (co-kernel approach) that handles all the realtime requirements separately (e.g., RTLinux, RTAI and Xenomai) [3][4][5]. Regarding latency issues, although RTAI and Xenomai offer lower latency than PREEMPT_RT, Linutronix tests show that the differences are not so significant, especially in real-world scenarios.…”

Section: Introductionmentioning

confidence: 99%

Performance Assessment of Linux Kernels with PREEMPT_RT on ARM-Based Embedded Devices

2021

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This work investigates the real-time performance of Linux kernels and distributions with a PREEMPT_RT real-time patch on ARM-based embedded devices. Experimental measurements, which are mainly based on heuristic methods, provide novel insights into Linux real-time performance on ARM-based embedded devices (e.g., BeagleBoard and RaspberryPi). Evaluations of the Linux real-time performance are based on specific real-time software measurement modules, developed for this purpose, and the use of a standard benchmark tool, cyclictest. Software modules were designed upon the introduction of a new response task model, an innovative aspect of this work. Measurements include the latency of response tasks at user and kernel space, the response on the execution of periodic tasks, the maximum sustained frequency and general latency performance metrics. The results show that in such systems the PREEMPT_RT patch provides more improved real-time performance than the default Linux kernels. The latencies and particularly the worst-case latencies are reduced with real-time support, thus making such devices running Linux with PREEMPT_RT more appropriate for use in time-sensitive embedded control systems and applications. Furthermore, the proposed performance measurements approach and evaluation methodology could be applied and deployed on other Linux-based real-time platforms.

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