1,720,967 research outputs found
Real-time and energy efficiency in Linux: theory and practice
No full textThe recent changes made in the Linux kernel aimed at achieving better energy efficiency through a tighter integration between the CPU scheduler and the frequency-scaling subsystem. However, in the original implementation, the frequency scaling mechanism was used only when there were no realtime tasks in execution. This paper shows how the deadline scheduler and the cpufreq subsystem have been extended to relax this constraint and implement an energy-aware realtime scheduling algorithm. In particular, we describe the design issues encountered when implementing the GRUB-PA algorithm on a real operating system like Linux. A set of experimental results on a multi-core ARM platform validate the effectiveness of the proposed implementation, which has been recently merged into the official Linux kernel
An implementation of a multiprocessor bandwidth reservation mechanism for groups of tasks
No full textAn Experimental Comparison of Different Real-Time Schedulers on Multicore Systems
No full textIn this work, an experimental comparison among the Rate Monotonic (RM) and Earliest Deadline First (EDF) multiprocessor real-time schedulers is performed, with a focus on soft real-time systems. We generated random workloads of synthetic periodic task sets and executed them on a big multi-core machine, using Linux as Operating System, gathering an extensive amount of data related to their exhibited performance under various real-time scheduling strategies. The comparison involves the fixed-priority scheduler for multiprocessors as available in the Linux kernel (with priorities set so as to achieve RM), and on our own implementation of EDF, both configured in global, partitioned and clustered mode. The impact of the various scheduling strategies on the performance of the applications, as well as the generated scheduling overheads, are compared presenting an extensive set of experimental results. These provide a comprehensive view of the performance achievable by the different schedulers under various workload conditions
A Linux-based Virtualized Solution Providing Computing Quality of Service to SDN-NFV Telecommunication Applications
No full textDeadline scheduling in the Linux kernel
No full textDuring 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
An implementation of the Bandwidth Inheritance Protocol in the Linux Kernel
No full textThe Resource Reservation (RR) framework has been proven very effective in the joint scheduling of hard real time and soft real time application in Open Systems. A fundamental problem in this context concerns the extension of the Resource Reservation approach to systems where tasks interact through shared resources.
The Bandwidth Inheritance (BWI) protocol was first proposed in [Lamastra G., Lipari G., Abeni L. (2001) A bandwidth inheritance algorithm for real-time task synchronization in open systems. In: Proc. 22nd IEEE Real-Time Systems Symposium] to preserve Bandwidth Isolation between independent groups of tasks, and to enable a schedulability analysis for hard real time tasks.
In this paper, we present the first implementation of the BWI protocol within the Linux kernel. We describe the protocol, the way it has been implemented in Linux, and we report some early experiments to measure its overhead. Our work is based on the SCHED_DEADLINE patch, a scheduling class for the Linux kernel that provides Resource Reservation using the Constant Bandwidth Server algorithm. The BWI implementation extends Linux's current implementation of the Priority Inheritance protocol, without affecting past design decisions. Our implementation is neutral to the underlying scheduling scheme and can be adopted in global, clustered and partitioned scheduling.
Results show agreement with theoretical analysis, and performance/overheads comparable with the current implementation of Priority Inheritance in Linux.
The work presented here has practical implications for applications running on Linux with SCHED_DEADLINE scheduling policy and share resources through mutex semaphores. In fact, the protocol guarantees temporal isolation between non-interacting threads, hence real-time guarantees are possible even where no a-priori information about tasks' scheduling parameters are available
Energy-aware real-time scheduling in the linux kernel
Full text linkThe recent changes made in the Linux kernel aim at achieving better energy efficiency through a tighter integration between the CPU scheduler and the frequency-scaling subsystem. However, in the current implementation, the frequency scaling mechanism is used only when there are no real-time tasks in execution. This paper shows how the deadline scheduler and the cpufreq subsystem can be extended to relax this constraint and implement an energy-aware real-time scheduling algorithm. In particular, we describe the design issues encountered when implementing the GRUB-PA algorithm on a real operating system like Linux. A set of experimental results on a multi-core ARM platform validate the effectiveness of the proposed implementation
On the Energy-Aware Partitioning of Real-Time Tasks on Homogeneous Multi-Processor Systems
No full textIn high-performance computing systems, efficient energy management is a key feature for keeping energy bills low and avoiding thermal dissipation problems, as well as for
controlling the application performance. This paper considers
the problem of partitioning and scheduling a set of real-time
tasks on a realistic hardware platform consisting of a number
of homogeneous processors. Several well-known heuristics are
compared to identify the approach that better reduces the overall
energy consumption of the entire system. Despite the actual state
Another well-known approach is the Dynamic Power Man-
of art, the approach which minimizes the number of active cores
is the most energy efficient
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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