A Fully Preemptive Multiprocessor Semaphore Protocol for Latency-Sensitive Real-Time Applications

Brandenburg, Björn B.

doi:10.1109/ecrts.2013.38

Cited by 21 publications

(5 citation statements)

References 24 publications

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“…Trace tools are frequently used in the analysis of real‐time Linux implementations . The main motivations for the utilization of trace, rather than alternatives such as logging and debugging, come from the fact that trace tools have as an objective low overhead and the ability of massively collecting and storing data during execution .…”

Section: Trace Timeflow: a New Trace Toolmentioning

confidence: 99%

Timing analysis of the PREEMPT RT Linux kernel

Oliveira

2015

Softw Pract Exp

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In the theory of real-time scheduling, tasks are described by mathematical variables, which are used in analytical models in order to prove schedulability of the system. On real-time Linux, tasks are computer programs, and Linux developers try to lower the latencies caused by the Linux kernel, trying to achieve faster response for the highest-priority task. Although both seek temporal correctness, they use different abstractions, which end up separating these efforts in two different worlds, making it hard for the Linux practitioners to understand and apply the formally proved models to the Linux kernel and for theoretical researchers to apply the restrictions imposed by Linux for the theoretical models. This paper traces a parallel between the theory of response-time analysis and the abstractions used in the Linux kernel. The contribution of this paper is threefold. We first identify the PREEMPT RT Linux kernel mechanisms that impact the timing of real-time tasks and map these impacts to the main abstractions used by the real-time scheduling theory. Then, we describe a customized trace tool, based on the existing trace infrastructure of the Linux kernel, that allows the measurement of the delays associated with the main abstractions of the real-time scheduling theory. Finally, we use this customized trace tool to characterize the timing lines resulting from the behavior of the PREEMPT RT Linux kernel.In addition to the function trace, there are other trace plugins, with emphasis on the function graph. The function graph traces the call and return of a function. To improve the understanding of the stack of functions, the output shows the indentation of the functions according to its position in the stack. This is an example of the execution of the function graph:An advantage of the function graph is the ability to determine the execution time of a particular function. It also makes the trace easy to follow, because of the indentation of functions. Ftrace allows the combined use of trace plugins and tracepoints.The tracer proposed in this article, denominated Trace Timeflow, was created based on the function graph tracer, in order to trace the relevant functions. It also uses tracepoints to trace important changes in the system state. Trace timeflowInitially, the new plugin was built as a copy of function graph. From this clone, changes were made to meet our needs. The first change was the fields to be displayed in the trace. Trace format.The format of the trace consists of six fields, as in the following example:The field TASK-PID identifies the task running, it displays the name of the process and its PID. The field PRIO displays the priority. Currently, Linux has 140 priorities, where priority 0 is the highest and 139 is the lowest. The real-time tasks use priorities from 0 to 99, with priorities from 100 to 139 used as time-sharing priorities.The field CPU displays the CPU where the task is running.TIMING ANALYSIS OF THE PREEMPT RT LINUX KERNEL 805 Inside the infinite loop created with for, the function pause(...

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Section: Trace Timeflow: a New Trace Toolmentioning

confidence: 99%

Timing analysis of the PREEMPT RT Linux kernel

Oliveira

2015

Softw Pract Exp

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“…MPCP and MSRP have been compared in a number of research works (with respect to the worst-case timing guarantees) with general consensus that MSRP performs best for short (global) critical sections and MPCP for large ones. A more detailed discussion on the design options and the characteristics of lock-based resource protection algorithms can be found in [8]. Wait-free mechanisms are an alternative option for preserving data consistency in multicore communication [12].…”

Section: State Of the Artmentioning

confidence: 99%

“…A task is assigned to the core where tryAssign returns the maximum least normalized slack (s). Like [8], tryAssign uses the Audsley's algorithm [2] to find a priority order of the tasks.…”

Section: Casr: Task Placement With Affinitymentioning

confidence: 99%

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Task placement and selection of data consistency mechanisms for real-time multicore applications

Al-bayati

Sun

Zeng

et al. 2015

21st IEEE Real-Time and Embedded Technology and Applications Symposium

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Multicores are today used in several automotive, controls and avionics systems supporting real-time functionality. When real-time tasks allocated on different cores cooperate through the use of shared communication resources, they need to be protected by mechanisms that guarantee access in a mutual exclusive way with bounded worst-case blocking time. Lock-based mechanisms such as MPCP and MSRP have been developed to fulfill this demand, and research papers are today tackling the problem of finding the optimal task placement in multicores while trying to meet the deadlines against blocking times. In this work, we provide a method that improves on existing task placement algorithms for systems that use MSRP to protect shared resources. Furthermore, we leverage an additional opportunity provided by wait-free methods as an alternative data consistency mechanism in those cases where the shared resource is communication or state memory. The selective use of waitfree communication can further extend the range of schedulable systems and consequently the design space, at the cost of memory.

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“…In the following, we summarize the mechanisms for data consistency in multicore systems and analyze the subset of mechanisms that can guarantee flow preservation. A classification of protocols with a detailed discussion can be found in [37]. Protocols for predictable access to nested global critical sections are discussed in [41].…”

Section: Introductionmentioning

confidence: 99%

Experimental Evaluation and Selection of Data Consistency Mechanisms for Hard Real-Time Applications on Multicore Platforms

Zeng

Natale

et al. 2014

IEEE Trans. Ind. Inf.

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Multicore platforms are increasingly used in real-time embedded applications. In control systems, including automotive, avionics, and automation, resources shared by tasks on different cores need to be protected by mechanisms that guarantee access in a mutually exclusive way with bounded worst case blocking time. The evaluation of the tradeoffs among the possible protocols for mutual exclusion requires an estimate of their implementation overheads. In this paper, we summarize the possible protection mechanisms and provide code implementations in real-time operating systems executing on a multicore platform. We discuss the tradeoffs among the different mechanisms based on experimental evaluation of their memory and timing overheads as well as their impact on system schedulability. We propose a heuristic algorithm to select the optimal combination of mechanisms for shared resources in systems with time constraints to minimize their memory requirements. The effectiveness of the optimization procedure is demonstrated by synthetic systems as well as industrial case studies.

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A Fully Preemptive Multiprocessor Semaphore Protocol for Latency-Sensitive Real-Time Applications

Cited by 21 publications

References 24 publications

Timing analysis of the PREEMPT RT Linux kernel

Timing analysis of the PREEMPT RT Linux kernel

Task placement and selection of data consistency mechanisms for real-time multicore applications

Experimental Evaluation and Selection of Data Consistency Mechanisms for Hard Real-Time Applications on Multicore Platforms

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