1,720,961 research outputs found
Response-Time Analysis for Globally Scheduled Symmetric Multiprocessor Platforms
No full textIn the last years, a progressive migration from single processor chips to multi-core computing devices has taken place in the general-purpose and embedded system market. The development of multi-processor systems is already a core activity for the most important hardware companies. A lot of different solutions have been proposed to overcome the physical limits of single core devices and to address the increasing computational demand of modern multimedia applications. The real-time community followed this trend with an increasing number of results adapting the classical scheduling analysis to parallel computing systems. This paper will contribute to refine the schedulability analysis for symmetric multi-processor (SMP) real-time systems composed by a set of periodic and sporadic tasks. We will focus on both fixed and dynamic priority global scheduling algorithms, where tasks can migrate from one processor to another during execution. By increasing the complexity of the analysis, we will show that an improvement is possible over existing schedulability tests, significantly increasing the number of schedulable task sets detected. The added computational effort is comparable to the cost of techniques widely used in the uniprocessor case. We believe this is a reasonable cost to pay, given the intrinsically higher complexity of multi-processor devices
EDZL scheduling analysis
No full textA schedulability test is derived for the global Earliest Deadline Zero Laxity (EDZL) scheduling algorithm on a platform with multiple identical processors. The test is sufficient, but not necessary, to guarantee that a system of independent sporadic tasks with arbitrary deadlines will be successfully scheduled, with no missed deadlines, by the multiprocessor EDZL algorithm. Global EDZL is known to be at least as effective as global Earliest-Deadline-First (EDF) in scheduling task sets to meet deadlines. It is shown, by testing on large numbers of pseudo-randomly generated task sets, that the combination of EDZL and the new schedulability test is able to guarantee that far more task sets meet deadlines than the combination of EDF and known EDF schedulability tests.In the second part of the paper, an improved version of the EDZL-schedulability test is presented. This new algorithm is able to efficiently exploit information on the slack values of interfering tasks, to iteratively refine the estimation of the interference a task can be subjected to. This iterative algorithm is shown to have better performance than the initial test, in terms of schedulable task sets detected
Schedulability Analysis of Global Scheduling Algorithms on Multiprocessor Platforms
Full text linkThis paper addresses the schedulability problem of periodic and sporadic real-time task sets with constrained deadlines preemptively scheduled on a multiprocessor platform composed by identical processors. We assume that a global work-conserving scheduler is used and migration from one processor to another is allowed during task lifetime. First, a general method to derive schedulability conditions for multiprocessor real-time systems will be presented. The analysis will be applied to two typical scheduling algorithms: Earliest Deadline First (EDF) and Fixed Priority (FP). Then, the derived schedulability conditions will be tightened, refining the analysis with a simple and effective technique that significantly improves the percentage of accepted task sets. The effectiveness of the proposed test is shown through an extensive set of synthetic experiments
Improved schedulability analysis of EDF on multiprocessor platforms
No full textMultiprocessor hardware platforms are now being considered for embedded systems, due to their high computational power and little additional cost when compared to single processor systems. When scheduling real-time applications on multiprocessor platforms, a possibility is to use global scheduling, where a scheduling algorithm dynamically assign tasks to processors, and tasks can migrate from one processor to another during their execution. In this paper, we tackle the problem of schedulability analysis of sporadic tasks in global scheduling systems, where the scheduler is the earliest deadline first (EDF) algorithm. We provide two main contributions. First, we show that two recently proposed tests perform poorly when the task set contains heavy tasks (i.e. tasks with high utilization). We also show that neither test dominates the other. As a second contribution, we introduce a new schedulability test that improves significantly the percentage of accepted task sets, especially when considering task sets containing heavy tasks. We show the effectiveness of the proposed test through an extensive set of experiments
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
New schedulability tests for real-time task sets scheduled by deadline monotonic on multiprocessors
No full textIn this paper, we address the problem of schedulability analysis of a set of real-time periodic (or sporadic) tasks on multiprocessor hardware platforms, under fixed priority global scheduling. In a multiprocessor system with M processors, a global scheduler consists of a single queue of ready tasks for all processors, and the scheduler selects the first M tasks to execute on the M processors. We allow preemption and migration of tasks between processors.This paper presents two different contributions. First, we derive a sufficient schedulability test for periodic and sporadic task system scheduled with fixed priority when priorities are assigned according to Deadline Monotonic. This test is efficient when dealing with heavy tasks (i.e. tasks with high utilization). Then, we develop an independent analysis for preperiod deadline systems. This leads to a new schedulability test with density and utilization bounds that are tighter than the existing ones
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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