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<p>The popularity of Linux in embedded systems has grown because of its reliability, flexibility, and performance. To ensure these systems meet specific real-time requirements, such as deadlines and throughput, Linux provides support for real-time schedulers and the PREEMPT_RT patch. However, while these tools prioritize high-priority tasks, they can inadvertently compromise the performance of other tasks. Completely Fair Scheduling (CFS) has served as the default scheduling policy in Linux until recently. The CFS is based on the principle that all runnable tasks should share the processor fairly, which helps balance task performance with overall system responsiveness. Despite its benefits, there has been no established method to assess whether real-time requirements are met under CFS. This paper introduces a novel analysis method to estimate the worst-case response time (WCRT) of tasks under CFS, providing a new solution for running real-time tasks in embedded Linux systems. Due to the dynamic nature of CFS, traditional WCRT analysis techniques are not applicable directly. Our technique analyzes how tasks sharing the same processor affect each other, focusing on their <i>vruntime</i>. By examining the bounds of vruntime variation and calculating the maximum interference from other tasks, we effectively estimate the WCRT. We also introduce algorithms that assign the <i>nice</i> values to tasks based on our proposed WCRT analysis technique, ensuring that the real-time requirements are met. We validate the proposed approach through comparative experiments using both a self-developed CFS simulator and an actual Linux system. Our simulator allows for rapid simulations and efficient exploration of various execution scenarios. Through extensive experiments, we empirically validate that our proposed analysis method is efficient with an acceptable level of overestimation. These make it a valuable tool for system verification and design optimization in Linux-based real-time systems.</p>

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Worst case response time analysis for completely fair scheduling in Linux systems

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年3月28日

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  • Kyonghwan Yoon,
  • EunJin Jeong,
  • Woosuk Kang,
  • Jonghyun Choe,
  • Soonhoi Ha

摘要

The popularity of Linux in embedded systems has grown because of its reliability, flexibility, and performance. To ensure these systems meet specific real-time requirements, such as deadlines and throughput, Linux provides support for real-time schedulers and the PREEMPT_RT patch. However, while these tools prioritize high-priority tasks, they can inadvertently compromise the performance of other tasks. Completely Fair Scheduling (CFS) has served as the default scheduling policy in Linux until recently. The CFS is based on the principle that all runnable tasks should share the processor fairly, which helps balance task performance with overall system responsiveness. Despite its benefits, there has been no established method to assess whether real-time requirements are met under CFS. This paper introduces a novel analysis method to estimate the worst-case response time (WCRT) of tasks under CFS, providing a new solution for running real-time tasks in embedded Linux systems. Due to the dynamic nature of CFS, traditional WCRT analysis techniques are not applicable directly. Our technique analyzes how tasks sharing the same processor affect each other, focusing on their vruntime. By examining the bounds of vruntime variation and calculating the maximum interference from other tasks, we effectively estimate the WCRT. We also introduce algorithms that assign the nice values to tasks based on our proposed WCRT analysis technique, ensuring that the real-time requirements are met. We validate the proposed approach through comparative experiments using both a self-developed CFS simulator and an actual Linux system. Our simulator allows for rapid simulations and efficient exploration of various execution scenarios. Through extensive experiments, we empirically validate that our proposed analysis method is efficient with an acceptable level of overestimation. These make it a valuable tool for system verification and design optimization in Linux-based real-time systems.