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 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 Open Access Performance-effective and low-complexity task scheduling for heterogeneous computing(IEEE COMPUTER SOC, 2002-03) TOPCUOĞLU, HALUK RAHMİ; Topcuoglu, H; Hariri, S; Wu, MYEfficient application scheduling is critical for achieving high performance in heterogeneous computing environments. The application scheduling problem has been shown to be NP-complete in general cases as well as in several restricted cases. Because of its key importance, this problem has been extensively studied and various algorithms have been proposed in the literature which are mainly for systems with homogeneous processors. Although there are a few algorithms in the literature for heterogeneous processors, they usually require significantly high scheduling costs and they may not deliver good quality schedules with lower costs. In this paper, we present two novel scheduling algorithms for a bounded number of heterogeneous processors with an objective to simultaneously meet high performance and fast scheduling time, which are called the Heterogeneous Earliest-Finish-Time (HEFT) algorithm and the Critical-Path-on-a-Processor (CPOP) algorithm. The HEFT algorithm selects the task with the highest upward rank value at each step and assigns the selected task to the processor, which minimizes its earliest finish time with an insertion-based approach. On the other hand, the CPOP algorithm uses the summation of upward and downward rank values for prioritizing tasks. Another difference is in the processor selection phase, which schedules the critical tasks onto the processor that minimizes the total execution time of the critical tasks. In order to provide a robust and unbiased comparison with the related work, a parametric graph generator was designed to generate weighted directed acyclic graphs with various characteristics. The comparison study, based on both randomly generated graphs and the graphs of some real applications, shows that our scheduling algorithms significantly surpass previous approaches in terms of both quality and cost of schedules, which are mainly presented with schedule length ratio, speedup, frequency of best results, and average scheduling time metrics.Publication Open Access Studying error propagation on application data structure and hardware(2022-11-01) ÖZTÜRK, ZUHAL; TOPCUOĞLU, HALUK RAHMİ; ÖZTÜRK Z., TOPCUOĞLU H. R., Kandemir M. T.As technology scales, transistors become smaller and aggressive power optimization techniques combined with high operation frequencies and performance-enhancing microarchitectural techniques are employed to achieve increasingly higher performance and power efficiencies. Unfortunately, these developments make the modern systems more vulnerable to soft errors, which are becoming a critical issues in both hardware and software domains. Motivated by this observation, in this work, we propose, implement, and evaluate two error propagation metrics in order to characterize error propagation at both software and hardware levels. The first metric aims to measure error propagation on program data structures, whereas the second one measures the fraction of corrupted locations in the cache memory structure for a given period of time. We evaluate our proposed metrics by performing an empirical study of two application programs using both single-threaded and multi-threaded executions, and varying various experimental parameters such as thread count, error rate, location of errors, and architectural parameters. Our extensive experimental analysis reveals that error propagation over program data structures is highly dependent on application behavior.Further, depending on the cache parameters used, propagation of errors on cache can exhibit different patterns. This paper also discusses how our observed error propagation trends in program data structures and data caches are correlated with each other, focusing in particular on the differences in error propagation speeds in application data structures and data caches.Publication Open Access Dynamic multi-objective evolutionary algorithms in noisy environments(2023-07-01) TOPCUOĞLU, HALUK RAHMİ; Sahmoud S., TOPCUOĞLU H. R.Real-world multi-objective optimization problems encounter different types of uncertainty that may affect the quality of solutions. One common type is the stochastic noise that contaminates the objective functions. Another type of uncertainty is the different forms of dynamism including changes in the objective functions. Although related work in the literature targets only a single type, in this paper, we study Dynamic Multi-objective Optimization problems (DMOPs) contaminated with stochastic noises by dealing with the two types of uncertainty simultaneously. In such problems, handling uncertainty becomes a critical issue since the evolutionary process should be able to distinguish between changes that come from noise and real environmental changes that resulted from different forms of dynamism. To study both noisy and dynamic environments, we propose a flexible mechanism to incorporate noise into the DMOPs. Two novel techniques called Multi-Sensor Detection Mechanism (MSD) and Welford-Based Detection Mechanism (WBD) are proposed to differentiate between real change points and noise points. The proposed techniques are incorporated into a set of Dynamic Multi-objective Evolutionary Algorithms (DMOEAs) to analyze their impact. Our empirical study reveals the effectiveness of the proposed techniques for isolating noise from real dynamic changes and diminishing the noise effect on performance.