Defects of the POSIX Sporadic Server and How to Correct Them

Stanovich, Mark; Baker, Theodore P.; Wang, An-I; Harbour, Michael González

doi:10.1109/rtas.2010.34

Cited by 27 publications

(17 citation statements)

References 15 publications

(31 reference statements)

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“…In Quest, Main VCPUs are by default configured as Sporadic Servers. We use the algorithm proposed by Stanovich et al [25] that corrects for early replenishment and budget amplification in the POSIX specification. Fixed priorities are used rather than dynamic priorities (e.g., associated with deadlines) so that we can treat the entire system as a collection of equivalent periodic tasks scheduled by a rate-monotonic scheduler (RMS) [11].…”

Section: Vcpu Scheduling Subsystemmentioning

confidence: 99%

“…The Sporadic Server policy for Main VPUs is based on that described by Stanovich et al [25]. In Algorithm 3 the VCPU has reached the end of a timeslice, so the usage counter is updated and budget-check is invoked to update the replenishment queue.…”

Section: Algorithm 2 Wakeupmentioning

confidence: 99%

“…Our Sporadic Server approach is based on that described by Stanovich et al [25], which corrects for defects in the POSIX specification. This type of server supports the fragmentation of resource budget over time.…”

Section: Related Workmentioning

confidence: 99%

“…In an attempt to provide temporal isolation and improved system predictability, we modified Linux to support a series of bandwidth preserving servers based on Deferrable and Sporadic Server policies [23,25]. Rather than changing existing APIs, such as POSIX, so that explicit time-constraints are placed on system service requests, we designed an architecture based around the notion of a "virtual CPU" (VCPU).…”

Section: Introductionmentioning

confidence: 99%

“…Algorithms 11, 12, and 13 are based on Stanovich et al [25]. These listings include fixes to minor errors we discovered in the original description.…”

mentioning

confidence: 99%

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Virtual-CPU Scheduling in the Quest Operating System

Danish

West

2011

2011 17th IEEE Real-Time and Embedded Technology and Applications Symposium

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Section: Vcpu Scheduling Subsystemmentioning

confidence: 99%

Section: Algorithm 2 Wakeupmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Algorithms 11, 12, and 13 are based on Stanovich et al [25]. These listings include fixes to minor errors we discovered in the original description.…”

mentioning

confidence: 99%

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Virtual-CPU Scheduling in the Quest Operating System

Danish

West

2011

2011 17th IEEE Real-Time and Embedded Technology and Applications Symposium

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Deadline scheduling in the Linux kernel

et al. 2015

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During the last decade, there has been a considerable interest in using Linux in real-time systems, especially for industrial control. The simple and elegant design of Linux guarantees reliability and very good performance, while its open-source license allows to modify and change the source code according to the user needs. However, Linux has been designed to be a general-purpose operating system. Therefore, it presents some issues like unpredictable latencies and limited support for real-time scheduling. In this paper, we present our experience in the design and implementation of the real-time scheduler that has been recently included in the Linux kernel. The scheduler is based on the Resource Reservation paradigm, which allows to enforce temporal isolation between the running tasks. We describe the genesis of the project, the challenges we have encountered, the implementation details and the API offered to the programmers. Then, we show the experimental results measured on a real hardware.has concerned the optimization of the average throughput (i.e. the amount of 'useful work' performed by the system in the unit of time) instead of meeting the timing constraints of each running application. As a result, the standard Linux kernel does not provide good real-time performance (i.e. low kernel latencies) or other features needed for supporting real-time applications (for example, advanced scheduling / resource management algorithms).In this paper, we describe a real-time scheduler for the CPU that we have recently included in Linux. The paper is organized as follows. In Section 2, we present the previous work about real-time on Linux. In Section 3, we describe the scheduling algorithm, the implementation details as well as the API offered to the programmer. Then, in Section 4, we provide some experimental results on a real hardware. Finally, in Section 5, we state our conclusions and we provide information about the future work. RELATED WORKIn the last decade, several (sometimes orthogonal) mechanisms have been proposed to add real-time capabilities to the Linux kernel. These mechanisms can be grouped in the following classes [1].Hardware Abstraction Layers (HALs). The first technique consists on reducing the kernel latency through a small abstraction layer (also called hypervisor), which virtualizes the hardware exposed to the Linux kernel [2]. This layer takes full control of the hardware resources (mainly, interrupts and system timers) and directly handles the real-time tasks at a higher priority than Linux. The Linux kernel is thus scheduled by the HAL as a low-priority task. The real-time applications cannot use functionalities provided by the Linux kernel, unless by temporarily loosing their real-time guarantees.This approach, originally introduced by Finite State Machine Labs with real-time Linux (RTLinux) [3], then acquired by Wind River [4], is now provided by two community-driven projects. The Real-Time Application Interface (RTAI) project [5], started in 1997, has developed the Adeos kernel [6] as a rep...

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Handling Non-Periodic Events in Real-Time Java Systems

Masson¹,

Midonnet²

2011

Distributed, Embedded and Real-Time Java Systems

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Defects of the POSIX Sporadic Server and How to Correct Them

Cited by 27 publications

References 15 publications

Virtual-CPU Scheduling in the Quest Operating System

Virtual-CPU Scheduling in the Quest Operating System

Deadline scheduling in the Linux kernel

Handling Non-Periodic Events in Real-Time Java Systems

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