Person: TOPCUOĞLU, HALUK RAHMİ
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TOPCUOĞLU
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HALUK RAHMİ
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Publication Open Access Quantifying the impact of data replication on error propagation(2022-09-01) ÖZTÜRK, ZUHAL; TOPCUOĞLU, HALUK RAHMİ; ÖZTÜRK Z., TOPCUOĞLU H. R. , Kandemir M. T.Various technological developments in the microprocessor world make modern computing systems more vulnerable to soft errors than in the past, and consequently fault tolerance techniques are becoming increasingly important in various application domains. While in general fault tolerance methods are known to achieve high levels of reliability, they can also introduce significant performance, energy, and memory overheads, which can be reduced by employing such techniques selectively, as opposed to indiscriminately. Data Replication is used to prevent error propagation across hardware components and application program data structures by replicating application program\"s data. When using data replication, many factors need to be taken into account, including which data structures/elements to replicate, how many times to replicate a given data element, and which threads to protect (in a multithreaded application). These and similar factors define what can be termed as \"replication space\". This study defines a replication space, and systematically explores protection techniques of various strengths/degrees, quantifying their impacts on memory consumption, performance, and error propagation. Our experimental analysis reveals that different degrees of protection levels bring different outcomes based on the application specifics. In particular, while error propagation is limited, to a certain extent, when employing data replication in multithreaded applications where the thread do not communicate/share data much, the speed of error propagation across threads can be quite fast in applications where threads are more tightly coupled. Additionally, our results indicate that in certain cases where error propagation is low, the effect of data replication on error propagation can be negligible.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 Neural network based multi-objective evolutionary algorithm for dynamic workflow scheduling in cloud computing(ELSEVIER, 2020) TOPCUOĞLU, HALUK RAHMİ; Ismayilov, Goshgar; Topcuoglu, Haluk RahmiWorkflow scheduling is a largely studied research topic in cloud computing, which targets to utilize cloud resources for workflow tasks by considering the objectives specified in QoS. In this paper, we model dynamic workflow scheduling problem as a dynamic multi-objective optimization problem (DMOP) where the source of dynamism is based on both resource failures and the number of objectives which may change over time. Software faults and/or hardware faults may cause the first type of dynamism. On the other hand, confronting real-life scenarios in cloud computing may change number of objectives at runtime during the execution of a workflow. In this study, we propose a prediction based dynamic multi-objective evolutionary algorithm, called NN-DNSGA-II algorithm, by incorporating artificial neural network with the NSGA-II algorithm. Additionally, five leading non-prediction based dynamic algorithms from the literature are adapted for the dynamic workflow scheduling problem. Scheduling solutions are found by the consideration of six objectives: minimization of makespan, cost, energy and degree of imbalance; and maximization of reliability and utilization. The empirical study based on real-world applications from Pegasus workflow management system reveals that our NN-DNSGA-II algorithm significantly outperforms the other alternatives in most cases with respect to metrics used for DMOPs with unknown true Pareto-optimal front, including the number of non-dominated solutions, Schott's spacing and Hypervolume indicator. (C) 2019 Elsevier B.V. All rights reserved.Publication Open Access Network Congestion Aware Multiobjective Task Scheduling in Heterogeneous Fog Environments(2023-01-01) TOPCUOĞLU, HALUK RAHMİ; Altin L., TOPCUOĞLU H. R., Gurgen F. S.Task scheduling on fog environments surges new challenges compared to scheduling on conventional cloud computing. Various levels of heterogeneity and dynamism cause task scheduling problem is more challenging for fog computing. In this study, we present a multiobjective task scheduling model with a total of five objectives and propose a multiobjective multirank (MOMRank) scheduling algorithm for fog computing. The performance of the proposed strategy is assessed with well-known multiobjective metaheuristics [the nondominated sorting genetic algorithm II (NSGA-II) and the Strength Pareto Evolutionary Algorithm 2 (SPEA2)] and a widely used algorithm from the literature, the multiobjective heterogeneous earliest finish time (MOHEFT) algorithm using three common multiobjective metrics. Additionally, we incorporate two task clustering mechanisms to the algorithms in order to improve data transmissions on interconnection networks. Results of empirical evaluations given in performance profiles over all problem instances validate significance of both our algorithm and the integrated extensions for diminishing data transfer costs.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.
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