Jelica Protic

A survey of distributed shared memory systems

Distributed shared memory (DSM) systems have attracted considerable research efforts recently, since they combine the advantages of two different computer classes: shared memory multiprocessors and distributed systems. The most important one is the use of shared memory programming paradigm on physically distributed memories. One possible classification taxonomy, which includes two basic criteria and a number of related characteristic, is proposed and described. According to the basic classification criteria-implementation level of DSM mechanism-systems are organized into three groups: hardware, software, and hybrid DSM implementations. The paper also presents an almost exhaustive survey of the existing solutions in an uniform manner, presenting their DSM mechanisms and issues of importance for various DSM systems and approaches.<<ETX>>

Web Performance Evaluation for Internet of Things Applications

An area of intensive research under the umbrella of the Internet of Things (IoT) has resulted in intensive proliferation of globally deployed sensor devices that provide a basis for the development of different use-case applications working with real-time data and demanding a rich user interface. Overcoming the lack of the standard HTML platform, HTML5 specifications WebSocket and Canvas graphics strongly supported the development of rich real-time applications. Such support has been offered by browser plug-ins such as Adobe Flash and Microsoft Silverlight for years. In order to provide a deep insight into IoT Web application performance, we implemented two test applications. In the first application, we measured latencies induced by different communication protocols and message encodings, as well as graphics rendering performance, while comparing the performance of different Web platform implementations. In the second application, we compared Web performance of IoT messaging protocols such as MQTT, AMQP, XMPP, and DDS by measuring the latency of sensor data message delivery and the message throughput rate. Our tests have shown that although Adobe Flash has the best performance at the moment, HTML5 platform is also very capable of running real-time IoT Web applications, whereas Microsoft Silverlight is noticeably behind both platforms. On the other hand, MQTT is the most appropriate messaging protocol for a wide set of IoT Web applications. However, IoT application developers should be aware of certain MQTT message broker implementation shortcomings that could prevent the usage of this protocol.

test: tools for evaluation of students' tests-a development experience

The purpose of the project that we describe in this paper is to provide teachers with efficient means of generating and scoring tests with multiple choice answers, inevitable in evaluating students knowledge at massive examinations. The idea is to maintain a database containing classified test questions, together with precisely defined criteria for selecting questions for an exam. A particular test can be composed automatically, or semiautomatically with active participation of the teacher. The final test document is produced in multiple versions, which represent various permutations of questions and answers. For each version, an answer key is also produced, which is used by an automatic scoring tool, that supports arbitrary hand-held or flat-bed scanner, for scanning answer sheets. This paper describes a set of software tools that we developed, in order to provide teachers with the efficient assistance in this process, on the commonly available PCs running Windows.

Scowl: a tool for characterization of parallel workload and its use on SPLASH-2 application suite

Concentrates on the problem of defining and measuring parameters that characterize typical behavior of parallel applications targeted to distributed shared memory (DSM) systems and shared-memory multiprocessors (SMPs). These parameters can be used as input to various models for performance evaluation in this research area. Furthermore, typical application behaviors can be recognized, which can help to generate new ideas for improvements to memory consistency protocols, adapting them to specific application characteristics. Our study encompasses a variety of parameters, such as frequencies of operations of various access types (private read/writes, shared read/writes, lock operations, barrier operations), the average number of accessed blocks per interval, the average number of modified words, etc. The results presented in this paper are based on the SPLASH-2 (Stanford Parallel Applications for SHared Memory) application suite. The developed instrumentation tool Scowl, along with the applied simulation environment Limes, are publicly available and applicable for performing measurements on other parallel applications as well.

Memory consistency models for shared memory multiprocessors and DSM systems

The use of systems with multiple processors that support shared memory programming paradigm is rapidly increasing nowadays. Possible buffering, pipelining, and optimization of shared memory accesses, as well as the existence of multiple copies of shared variables in these systems, may cause specific implications that can not be understood just as an intuitive extension of an uniprocessor memory model. Therefore, the memory consistency model formally specifies the memory system behavior to be expected by the programmer. This paper reveals the essence of several memory consistency models: sequential, processor, weak, release (with eager and lazy implementation), and entry. It also provides definitions and a set of examples that underline differences between particular models. Results of several performance evaluation studies are also discussed.

Self-similar cross-traffic analysis as a foundation for choosing among active available bandwidth measurement strategies

Among the many active, available bandwidth estimation tools and methods that have appeared recently in the literature, none has emerged that is accurate and robust enough to function in different networking environments. One of the main reasons for this problem is the highly variable statistical nature of network traffic. We present a novel theoretical method for active measurement strategy analysis through self-similar process sampling analysis. The results obtained show a relationship between the main parameters in the measurement procedure, such as the number of samples, sample length, and sample distance. The study suggests that accurate measurements require the use of many samples and thus long measurement procedures, sometimes on the order of several minutes, depending on the amount of cross traffic. Additionally, through the analysis of several existing Internet packet traces, we recommend that the minimum single sample probe stream length must be longer than the average cross traffic interarrival. Following these findings, we propose a new method for available bandwidth estimation that has shown significant accuracy under different network setups.

CISC versus RISC processors for graphics: a simulation study

Abstract This paper summarizes the results of a simulation study of single processors architectures for graphics. The entire work is done from point-of-view of RISC/CISC style classification. A comparison between various categories is evaluated using HDL description of representative processors, as well as simulations based on ENDOT simulation tools.

Intelligent crawler for web forums based on improved regular expressions

In this paper, we present the development and characteristics of a specialized Web-scale forum crawler. The main idea is to crawl relevant forum content from the Web with minimal server resource consumption, and to organize crawled content into logical units, in order to make it easier for further processing and analysis. Forum posts contain relevant information that are of interest to forum crawler. Although forums have different designs, and are built on different technologies, they always have identical logic navigation that connects homepage and particular posts through forum lists and threads by specific URLs. Considering this common implicit navigation, we have optimized Web crawling problem to be URL-type recognition problem. URL-type database and regular expressions are used in order to achieve URL-type recognition. These regular expressions are expanded with special custom characters and commands that gave this forum crawler advantage over other Web based crawlers. The results shown in this paper are obtained by crawling a set of Web forums with different technology, location and design. Each test compared the results obtained by standard Web based crawler and our specialized forum crawler. Our test results show that by crawling only specific data and URL paths on the forum, we have managed to reduce the time of crawling and to achieve lower server resources consumption.

Remote control of industrial robot lola 50 using wireless communication and android device

Android platform based devices are powerful mobile computers with a rich variety of built-in sensors and permanent Internet connectivity. Because of its powerful capabilities, as well as open architecture, they became promising candidates for a number of industrial applications. This paper describes the process of implementation and use of application for remote control of industrial robot Lola 50, in manual mode, using the Android mobile phone and wireless communication.

A comparison of three protocols for entry consistency maintenance based on MVA algorithm

In a distributed shared memory (DSM) system that implements an entry consistency model, shared data must be explicitly associated to a synchronization variable, and it can be accessed only in critical sections protected by that specific synchronization variable. The authors propose three protocols for entry consistency maintenance, ECU, ECI, and ECHBP, and they identify costs introduced by each of these consistency protocols, such as communication, processing and synchronization latencies. In order to determine synchronization latency we use a modified version of the MVA algorithm, while communication and processing latencies depend on an applications access behavior expressed by a probabilistic model. Finally, we determine processing power (e.g. speedup) of a system with N processors, taking into account communication, processing and synchronization latencies. In this way, we build a model for analytical comparison of the proposed protocols for a wide range of input parameters.