1,721,071 research outputs found
Limited preemption EDF scheduling of sporadic task systems
No full textThe optimality of the Earliest Deadline First scheduler for uniprocessor systems is one of the main reasons behind the popularity of this algorithm among real-time systems. The ability of fully utilizing the computational power of a processing unit however requires the possibility of preempting a task before its completion. When preemptions are disabled, the schedulability overhead could be significant, leading to deadline misses even at system utilizations close to zero. On the other hand, each preemption causes an increase in the runtime overhead due to the operations executed during a context switch and the negative cache effects resulting from interleaving tasks' executions. These factors have been often neglected in previous theoretical works, ignoring the cost of preemption in real applications. A hybrid limited-preemption real-time scheduling algorithm is derived here, that aims to have low runtime overhead while scheduling all systems that can be scheduled by fully preemptive algorithms. This hybrid algorithm permits preemption where necessary for maintaining feasibility, but attempts to avoid unnecessary preemptions during runtime. The positive effects of this approach are not limited to a reduced runtime overhead, but will be extended as well to a simplified handling of shared resources
Tests for global EDF schedulability analysis
No full textSeveral schedulability tests have been proposed for global EDF scheduling on identical multiprocessors. All these tests are sufficient, rather than exact. These different tests were, for the most part, independently developed. The relationships among such tests have not been adequately investigated, so that it is difficult to understand which test is most appropriate in a particular given scenario. This paper represents an attempt to remedy this, by means of three major contributions. First, we summarize the main existing results for the schedulability analysis of multiprocessor systems scheduled with global edf, showing, when possible, existing dominance relations. We compare these algorithms taking into consideration different aspects, namely, run-time complexity, average performances over randomly generated workloads, sustainability properties and speedup factors. Second, based on this comparative evaluation we propose a recommended approach to schedulability analysis, that suggests a particular order in which to apply preexisting tests, thereby accomplishing both good provable performance and good behavior in practice. And finally, we propose a further improvement to one of these preexisting tests to improve its run-time performance by an order of magnitude, while completely retaining its ability to correctly identify schedulable systems
Resource holding times: Computation and Optimization
No full textIn scheduling hard-real-time systems, the primary objective is to meet all deadlines. We study the scheduling of such systems with the secondary objective of minimizing the duration of time for which the system locks each shared resource. We abstract out this objective into the resource hold time (rht)—the largest length of time that may elapse between the instant that a system locks a resource and the instant that it subsequently releases the resource, and study properties of the rht. We present an algorithm for computing resource hold times for every resource in a task system that is scheduled using Earliest Deadline First scheduling, with resource access arbitrated using the Stack Resource Policy. We also present and prove the correctness of algorithms for decreasing these rht’s without changing the semantics of the application or compromising application feasibility
Resource-sharing servers for Open Environments
No full textWe study the problem of executing a collection of independently designed and validated task systems upon a common platform composed of a preemptive processor and additional shared resources. We present an abstract formulation of the problem and identify the major issues that must be addressed in order to solve this problem. We present and prove the correctness of algorithms that address these issues, and thereby obtain a design for an open real-time environment
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
Static-Priority Scheduling and Resource Hold Times
Full text linkThe duration of time for which each application locks each shared resource is critically important in composing multiple independently-developed applications upon a shared "open" platform. In a companion paper, we formally defined and studied the concept of resource hold time (RHT) - the largest length of time that may elapse between the instant that an application system locks a resource and the instant that it subsequently releases the resource. We extend the discussion and results from to systems scheduled using static-priority scheduling algorithms, with resource access arbitrated using stack resource policy (SRP), or priority ceiling protocol (PCP). We present a method to compute resource hold times for every resource, and an algorithm to decrease them without changing the semantics of the application or compromising application feasibility
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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