Person: TOPCUOĞLU, HALUK RAHMİ
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TOPCUOĞLU
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HALUK RAHMİ
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Publication Metadata only Thread vulnerability in parallel applications(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2012) TOPCUOĞLU, HALUK RAHMİ; Oz, Isil; Topcuoglu, Haluk Rahmi; Kandemir, Mahmut; Tosun, OguzContinuously reducing transistor sizes and aggressive low power operating modes employed by modern architectures tend to increase transient error rates. Concurrently, multicore machines are dominating the architectural spectrum today in various application domains. These two trends require a fresh look at resiliency of multithreaded applications against transient errors from a software perspective. In this paper, we propose and evaluate a new metric called the Thread Vulnerability Factor (TVF). A distinguishing characteristic of TVF is that its calculation for a given thread (which is typically one of the threads of a multithreaded application) does not depend on its code alone, but also on the codes of the threads that share resources and data with that thread. As a result, we decompose TVF of a thread into two complementary parts: local and remote. While the former captures the TVF induced by the code of the target thread, the latter represents the vulnerability impact of the threads that interact with the target thread. We quantify the local and remote TVF values for three architectural components (register file, ALUs, and caches) using a set of ten multithreaded applications from the Parsec and Splash-2 benchmark suites. Our experimental evaluation shows that TVF values tend to increase as the number of cores increases, which means the system becomes more vulnerable as the core count rises. We further discuss how TVF metric can be employed to explore performance-reliability tradeoffs in multicores. Reliability-based analysis of compiler optimizations and redundancy-based fault tolerance are also mentioned as potential usages of our TVF metric. (C) 2012 Elsevier Inc. All rights reserved.Publication Metadata only Scheduling opportunities for asymmetrically reliable caches(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2019) TOPCUOĞLU, HALUK RAHMİ; Arslan, Sanem; Topcuoglu, Haluk Rahmi; Kandemir, Mahmut Taylan; Tosun, OguzModern systems become more vulnerable to soft errors with technology scaling. Providing fault tolerance strategies on all structures in a system may lead to high energy consumption. Our framework with asymmetrically reliable caches with at least one protected core and several unprotected cores dynamically assigns the software threads executing critical code fragments to the protected core(s) with the FCFS-based algorithm. The framework can provide good reliability, performance, and power consumption trade-offs compared with the fully protected and unprotected systems. However, FCFS-based scheduling algorithm may degrade the system performance and unfairly slow down applications for some workloads. In this paper, a set of scheduling algorithms is proposed to improve both the system performance and fairness perspectives. Various static priority techniques that require preliminary information about the applications (such as their execution order, cache usage, number of requests sent to the protected core(s), and total burst time spent on the protected core(s)) are implemented and evaluated. On the other hand, dynamic priority techniques that target to equalize the total time spent of applications on the protected core(s) or the progress of the applications' requests are presented. Extensive evaluations using multi application workloads validate significant improvements of our static and dynamic priority scheduling techniques on system performance and fairness over the FCFS algorithm. (C) 2019 Elsevier Inc. All rights reserved.Publication Metadata only Impact of sensor-based change detection schemes on the performance of evolutionary dynamic optimization techniques(SPRINGER, 2018) TOPCUOĞLU, HALUK RAHMİ; Altin, Lokman; Topcuoglu, Haluk RahmiEvolutionary algorithms are among the most common techniques developed to address dynamic optimization problems. They either assume that changes in the environment are known a priori, especially for some benchmark problems, or detect these changes. On the other hand, detecting the points in time where a change occurs in the landscape is a critical issue. In this paper, we investigate the performance evaluation of various sensor-based detection schemes on the moving peaks benchmark and the dynamic knapsack problem. Our empirical study validates the performance of the sensor-based detection schemes considered, by using the average rate of correctly identified changes and number of sensors invoked to detect a change. We also propose a new mechanism to evaluate the capability of the detection schemes for determining severity of changes. Additionally, a novel hybrid approach is proposed by integrating the change detection schemes with evolutionary dynamic optimization algorithms in order to set algorithm-specific parameters dynamically. The experimental evaluation validates that our extensions outperform the reference algorithms for various characteristics of dynamism.Publication Metadata only Performance evaluation of evolutionary heuristics in dynamic environments(SPRINGER, 2012) TOPCUOĞLU, HALUK RAHMİ; Ayvaz, Demet; Topcuoglu, Haluk Rahmi; Gurgen, FikretIn recent years, there has been a growing interest in applying genetic algorithms to dynamic optimization problems. In this study, we present an extensive performance evaluation and comparison of 13 leading evolutionary algorithms with different characteristics on a common platform by using the moving peaks benchmark and by varying a set of problem parameters including shift length, change frequency, correlation value and number of peaks in the landscape. In order to compare solution quality or the efficiency of algorithms, the results are reported in terms of both offline error metric and dissimilarity factor, our novel comparison metric presented in this paper, which is based on signal similarity. Computational effort of each algorithm is reported in terms of average number of fitness evaluations and the average execution time. Our experimental evaluation indicates that the hybrid methods outperform the related work with respect to quality of solutions for various parameters of the given benchmark problem. Specifically, hybrid methods provide up to 24% improvement with respect to offline error and up to 30% improvement with respect to dissimilarity factor by requiring more computational effort than other methods.Publication Metadata only Reliability-aware core partitioning in chip multiprocessors(ELSEVIER, 2012) TOPCUOĞLU, HALUK RAHMİ; Oz, Isil; Topcuoglu, Haluk Rahmi; Kandemir, Mahmut; Tosun, OguzExecuting multiple applications concurrently is an important way of utilizing the computational power provided by emerging chip multiprocessor (CMP) architectures. However, this multiprogramming brings a resource management and partitioning problem, for which one can find numerous examples in the literature. Most of the resource partitioning schemes proposed to date focus on performance or energy centric strategies. In contrast, this paper explores reliability-aware core partitioning strategies targeting CMPs. One of our schemes considers both performance and reliability objectives by maximizing a novel combined metric called the vulnerability-delay product (VDP). The vulnerability component in this metric is represented with Thread Vulnerability Factor (TVF), a recently proposed metric for quantifying thread vulnerability for multicores. Execution time of the given application represents the delay component of the VDP metric. As part of our experimental analysis, proposed core partitioning schemes are compared with respect to normalized weighted speedup, normalized weighted reliability loss and normalized weighted vulnerability delay product gain metrics for various workloads of benchmark applications. (C) 2012 Elsevier B.V. All rights reserved.Publication Metadata only A user-assisted thread-level vulnerability assessment tool(WILEY, 2019) TOPCUOĞLU, HALUK RAHMİ; Oz, Isil; Topcuoglu, Haluk Rahmi; Tosun, OguzThe system reliability becomes a critical concern in modern architectures with the scale down of circuits. To deal with soft errors, the replication of system resources has been used at both hardware and software levels. Since the redundancy causes performance degradation, it is required to explore partial redundancy techniques that replicate the most vulnerable parts of the code. The redundancy level of user applications depends on user preferences and may be different for the users with different requirements. In this work, we propose a user-assisted reliability assessment tool based on critical thread analysis for redundancy in parallel architectures. Our analysis evaluates the application threads of a parallel program by considering their criticality in the execution and selects the most critical thread or threads to be replicated. Moreover, we extend our analysis by exploring critical regions of individual threads and execute redundantly only those regions to reduce redundancy overhead. Our experimental evaluation indicates that the replication of the most critical thread improves the system reliability more (up to 10% for blackscholes application) than the replication of any other thread. The partial thread replication based on critical region analysis also reduces the vulnerability of the system by considering a fine-grained approach.Publication Metadata only Evolutionary dynamic optimization techniques for marine contamination problem(Association for Computing Machinery, Inc, 2015) TOPCUOĞLU, HALUK RAHMİ; Altin L., Topcuoglu H.R., Ermis M.Marine pollution is the release of by-products that cause harm to natural marine ecosystems and one of the most important sources is the discharge of oil, ballast water from vessels. If the relevant technology is not available, alternative way to monitor environmental pollution is to use unmanned air vehicles (UAVs). Since the navigating vessels move in different directions and speeds, the determination of the tour that should be traveled by a UAV resembles to the dynamic traveling salesman problem (DTSP) in many aspects. This paper addresses a new type of DTSP, where targets can move in different directions with different speeds. The locations of all vessels can change due to changes in velocity that alters the length of all edges. Consequently, this problem has a higher complexity in comparison to classical DTSP presented in the literature. An empirical study is conducted to evaluate performance of selected evolutionary dynamic optimization techniques on solving the problem. © Copyright 2015 ACM.Publication Metadata only A Type Detection Based Dynamic Multi-objective Evolutionary Algorithm(SPRINGER INTERNATIONAL PUBLISHING AG, 2018) TOPCUOĞLU, HALUK RAHMİ; Sahmoud, Shaaban; Topcuoglu, Haluk Rahmi; Sim, K; Kaufmann, P; Ascheid, G; Bacardit, J; Cagnoni, S; Cotta, C; DAndreagiovanni, F; Divina, F; EsparciaAlcazar, AL; DeVega, FF; Glette, K; Hidalgo, JI; Hubert, J; Iacca, G; Kramer, O; Mavrovouniotis, M; Garcia, AMM; Nguyen, TT; Schaefer, R; Silva, S; Tonda, A; Urquhart, N; Zhang, MCharacterization of dynamism is an important issue for utilizing or tailoring of several dynamic multi-objective evolutionary algorithms (DMOEAs). One such characterization is the change detection, which is based on proposing explicit schemes to detect the points in time when a change occurs. Additionally, detecting severity of change and incorporating with the DMOEAs is another attempt of characterization, where there is only a few related works presented in the literature. In this paper, we propose a type-detection mechanism for dynamic multi-objective optimization problems, which is one of the first attempts that investigate the significance of type detection on the performance of DMOEAs. Additionally, a hybrid technique is proposed which incorporates our type detection mechanism with a given DOMEA. We present an empirical evaluation by using seven test problems from all four types and five performance metrics, which clearly validate the motivation of type detection as well as significance of our hybrid technique.Publication Metadata only A meta-heuristic based three-dimensional path planning environment for unmanned aerial vehicles(SAGE PUBLICATIONS LTD, 2013) TOPCUOĞLU, HALUK RAHMİ; Oz, Isil; Topcuoglu, Haluk Rahmi; Ermis, MuratUnmanned Aerial Vehicles (UAVs) are used for many missions, including weather reconnaissance, search and rescue assisting operations over seas and mountains, aerial photographing and mapping, fire detection, and traffic control. Autonomous operation of UAVs requires the development of control systems that can work without human support for long time periods. The path planners, which generate collision-free and optimized paths, are needed to provide autonomous operation capabilities to the UAVs. The optimization of the flight trajectory is a multi-objective problem dealing with variable terrain features as well as dynamic environment conditions. This paper presents a simulation environment for offline path planning of unmanned aerial vehicles on three-dimensional terrains. Our path planner aims to identify the shortest path and/or flight envelope in a given line of sight by avoiding terrain collisions, traveling on a path that stays within the restricted minimum and maximum distances above the terrain, traveling far from the specified threat zones, and maneuvering with an angle greater than the minimum curvature radius. We present two meta-heuristics (genetic algorithms and hyper-heuristics) in order to construct the paths for UAV navigation and compare our results with a reference work given in the literature. A comparative study over a set of terrains with various characteristics validates the effectiveness of the proposed meta-heuristics, where the quality of a solution is measured with the total cost of a constructed path, including the penalties of all constraints.Publication Metadata only Protecting code regions on asymmetrically reliable caches(Springer Verlag, 2016) TOPCUOĞLU, HALUK RAHMİ; Arslan S., Topcuoglu H.R., Kandemir M.T., Tosun O.Cache structures in a multicore system are considerably susceptible to soft errors. Protecting all caches using fault tolerance techniques has notable overheads on performance and power consumption. In this paper, we propose an enhanced protection mechanism for reliabilitybased critical code regions of the applications on asymmetrically reliable cores which have different error-tolerant cache structures. In this system, software threads which execute reliability-based critical code regions are mapped onto the protected cores, whereas the threads which execute noncritical regions are mapped to the unprotected ones, dynamically during the execution. Our experimental evaluations indicate that the proposed system improves Silent Data Corruption (SDC) rate by 66% with 22% performance loss and 1.2% more power consumption for selected applications relative to the unprotected caches on average. © Springer International Publishing Switzerland 2016.