1,721,079 research outputs found
Grain sensitive event scheduling in time warp parallel discrete event simulation
No full textSeveral scheduling algorithms have been proposed to determine the ne,rr event to be executed on a processor in a Time Warp parallel discrete event simulation. However none of them is specifically designed for simulations where the execution time (or granularity)for different ty,pes of events has large variance. In this paper we present a grain sensitive scheduling algorithm which addresses this problem. In our solution, the scheduling decision depends on both timestamp and granularity values with the aim at giving higher priority, to small grain events even if their timestamp is not the lowest one (i.e. the closest one to the commitment horizon of the simulation). This implicitly limits the optimism of the execution of large grain events that, if rolled back, would produce large waste of CPU time. The algorithm is adaptive in that it relies on the dynamic recalculation of the length of a simulated time window within which the timestamp of ally good candidate event for the scheduling falls in. if the window length is set to Zeta, then the algorithm behaves like the standard Lowest-Timestamp-First (LTF) scheduling algorithm. Simulation results of a classical benchmark in several different configurations are reported for a performance comparison with LTE These results demonstrate the effectiveness of our algorithm
A checkpointing-recovery scheme for Time Warp parallel simulation
No full textThis paper presents a checkpointing-recovery scheme for Time Warp parallel simulation. The scheme relies on a checkpointing protocol, namely mixed state saving, embedding both sparse and incremental state saving modes, and on a state recovery procedure embedding both forward and backward recovery modes. This scheme is a generalization of many previous solutions, which can be obtained as particular instances of it by selecting appropriate values for the checkpointing protocol parameters. We also present two regulating algorithms to adaptively tune the checkpointing protocol parameters, in order to make the protocol reacting to variable rollback behavior. A synthetic benchmark in several different configurations has been used for evaluating and comparing our scheme with previous solutions. The obtained data show that our solution allows faster execution and, in addition, keeps quite low the amount of memory used for recording state information; this allows the scheme to not adversely affect performance when memory is a critical resource. © 2001 Elsevier Science B.V
An architectural framework for analyzing tradeoffs between software security and performance
No full textThe increasing complexity of software systems entails large effort to jointly analyze their non-functional attributes in order to identify potential tradeoffs among them (e.g. increased availability can lead to performance degradation). In this paper we propose a framework for the architectural analysis of software performance degradation induced by security solutions. We introduce a library of UML models representing security mechanisms that can be composed with performance annotated UML application models for architecting security and performance critical systems. Composability of models allows to introduce different security solutions on the same software architecture, thus supporting software architects to find appropriate security solutions while meeting performance requirements. We report experimental results that validate our approach by comparing a model-based evaluation of a software architecture for management of cultural assets with values observed on the real implementation of the syste
Managing the evolution of a software architecture at minimal cost under performance and reliability constraints
No full textOn the Processor Scheduling Problem in Time Warp Synchronization
No full textTime Warp is a synchronization mechanism for parallel/distributed simulation. It allows logical processes (LPs) to execute events without the guarantee of a causally consistent execution. Upon the detection of a causality violation, rollback procedures recover the state of the simulation to a correct value. When a rollback occurs there are two primary sources of performance loss: (1) CPU time must be spent for the execution of the rollback procedures and (2) waste of CPU time arises from the invalidation of event executions. In this paper we present a general framework for the problem of scheduling the next LP to be run on a processor in Time Warp simulations. The framework establishes a class of scheduling algorithms having the twofold aim to keep low the CPU time for the execution of the rollback procedures and also to guarantee low waste of time due to event executions invalidated by rollback. The combination of these two aims should actually lead to short completion time of Time Warp simulations. We collocate existing scheduling algorithms within the framework, pointing out how they miss previous aims, at least partially. Then we instantiate a Window-based Grain Sensitive (WGS) scheduling algorithm relying on the framework, which pursues the above twofold aim. We also identify the proper conditions, associated with the simulation model execution, under which any algorithm exploiting the framework structure is expected to benefit the performance of the Time Warp mechanism. Empirical evidence from an experimental study of WGS on classical benchmarks and on a mobile communication system simulation fully confirms the theoretical outcomes
EASIER: An Evolutionary Approach for Multi-objective Software ArchItecturE Refactoring
No full textMulti-objective optimization has demonstrated, in the last few years, to be an effective paradigm to tackle different architectural problems, such as service selection, composition and deployment. In particular, multi-objective approaches for searching architectural configurations that optimize quality properties (such as performance, reliability and cost) have been introduced in the last decade. However, a relevant amount of complexity is introduced in this context when performance are considered, often due to expensive iterative generation of performance models and interpretation of results. In this paper we introduce EASIER (Evolutionary Approach for multi-objective Software archItecturE Refactoring), that is an approach for optimizing architecture refactoring based on performance and on the intensity of changes. We focus on the actionable aspects of architectural optimization, instead of merely searching over a set of alternatives. We also start to investigate on the potential influence of performance antipatterns on such process. We have implemented our approach on Æmilia ADL, so to carry out performance analysis and architecture refactoring within the same environment. We demonstrate the effectiveness and applicability of our approach through its experimentation on a case study
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
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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