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MPtostream:an OpenMP compiler for CPU-GPU heterogeneous parallel systems

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Science China(Information Sciences) 2012年第9期55卷 1961-1971页

作者： YANG XueJun,TANG Tao ,WANG GuiBin,JIA Jia & XU XinHai national laboratory for parallel and distributed processing,national University of Defense Technology,Changsha 410073,China national laboratory for parallel and distributed processing National University of Defense Technology Changsha China

In light of GPUs’ powerful floating-point operation capacity,heterogeneous parallel systems incorporating general purpose CPUs and GPUs have become a highlight in the research field of high performance computing(HPC).However,due to the complexity of programming on GPUs,porting a large number of existing scientific computing applications to the heterogeneous parallel systems remains a big challenge.The OpenMP programming interface is widely adopted on multi-core CPUs in the field of scientific computing.To effectively inherit existing OpenMP applications and reduce the transplant cost,we extend OpenMP with a group of compiler directives,which explicitly divide tasks among the CPU and the GPU,and map time-consuming computing fragments to run on the GPU,thus dramatically simplifying the transplantation.We have designed and implemented MPtoStream,a compiler of the extended OpenMP for AMD’s stream processing GPUs.Our experimental results show that programming with the extended directives deviates from programming with OpenMP by less than 11% modification and achieves significant speedup ranging from 3.1 to 17.3 on a heterogeneous system,incorporating an Intel Xeon E5405 CPU and an AMD FireStream 9250 GPU,over the execution on the Xeon CPU alone.

关键词： GPGPU stream OpenMP compiler

Superscalar communication: A runtime optimization for distributed applications

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Science China(Information Sciences) 2010年第10期53卷 1931-1946页

作者： LI HuiBa , LIU ShengYun, PENG YuXing, LI DongSheng, ZHOU HangJun & LU XiCheng national laboratory for parallel and distributed processing, national University of Defense Technology, Changsha 410073, China national laboratory for parallel and distributed processing National University of Defense Technology Changsha China

Building distributed applications is difficult mostly because of concurrency management. Existing approaches primarily include events and threads. Researchers and developers have been debating for decades to prove which is superior. Although the conclusion is far from obvious, this long debate clearly shows that neither of them is perfect. One of the problems is that they are both complex and error-prone. Both events and threads need the programmers to explicitly manage concurrencies, and we believe it is just the source of difficulties. In this paper, we propose a novel approach—superscalar communication, in which concurrencies are automatically managed by the runtime system. It dynamically analyzes the programs to discover potential concurrency opportunities; and it dynamically schedules the communication and the computation tasks, resulting in automatic concurrent execution. This approach is inspired by the idea of superscalar technology in modern microprocessors, which dynamically exploits instruction-level parallelism. However, hardware superscalar algorithms do not fit software in many aspects, thus we have to design a new scheme completely from scratch. Superscalar communication is a runtime extension with no modification to the language, compiler or byte code, so it is good at backward compatibility. Superscalar communication is likely to begin a brand new research area in systems software, which is characterized by dynamic optimization for networking programs.

关键词： network programming concurrency event thread superscalar

A fast successive over-relaxation algorithm for force-directed network graph drawing

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Science China(Information Sciences) 2012年第3期55卷 677-688页

作者： WANG YongXian & WANG ZhengHua national Key laboratory for parallel and distributed processing, national University of Defense Technology, Changsha 410073, China national Key laboratory for parallel and distributed processing National University of Defense Technology Changsha China

Force-directed approach is one of the most widely used methods in graph drawing research. There are two main problems with the traditional force-directed algorithms. First, there is no mature theory to ensure the convergence of iteration sequence used in the algorithm and further, it is hard to estimate the rate of convergence even if the convergence is satisfied. Second, the running time cost is increased intolerablely in drawing largescale graphs, and therefore the advantages of the force-directed approach are limited in practice. This paper is focused on these problems and presents a sufficient condition for ensuring the convergence of iterations. We then develop a practical heuristic algorithm for speeding up the iteration in force-directed approach using a successive over-relaxation (SOR) strategy. The results of computational tests on the several benchmark graph datasets used widely in graph drawing research show that our algorithm can dramatically improve the performance of force-directed approach by decreasing both the number of iterations and running time, and is 1.5 times faster than the latter on average.

关键词： graph drawing graph layout successive over-relaxation force-directed algorithm

Towards estimating expected sizes of probabilistic skylines

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Science China(Information Sciences) 2011年第12期54卷 2574-2584页

作者： YANG YongTao & WANG YiJie national Key laboratory for parallel and distributed processing, School of Computer, national University of Defense Technology, Changsha 410073, China national Key laboratory for parallel and distributed processing School of Computer National University of Defense Technology Changsha China

We consider the maximal vector problem on uncertain data, which has been recently posed by the study on processing skyline queries over a probabilistic data stream in the database context. Let D n be a set of n points in a d-dimensional space and q (0 < q 1) be a probability threshold; each point in D n has a probability to occur. Our problem is concerned with how to estimate the expected size of the probabilistic skyline, which consists of all the points that are not dominated by any other point in D n with a probability not less than q. We prove that the upper bound of the expected size is O(min{n, (- ln q)(ln n) d-1 }) under the assumptions that the value distribution on each dimension is independent and the values of the points along each dimension are distinct. The main idea of our proof is to find a recurrence about the expected size and solve it. Our results reveal the relationship between the probability threshold q and the expected size of the probabilistic skyline, and show that the upper bound is poly-logarithmic when q is not extremely small.

关键词： probabilistic skyline probabilistic data streams expected size

A logistic regression model for Semantic Web service matchmaking

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Science China(Information Sciences) 2012年第7期55卷 1715-1720页

作者： WEI DengPing 1 ,WANG Ting 1 & WANG Ji 2 1 School of Computer,national University of Defense Technology,Changsha 410073,China 2 national laboratory for parallel and distributed processing,Changsha 410073,China School of Computer National University of Defense Technology Changsha China national laboratory for parallel and distributed processing Changsha China

Semantic Web service matchmaking,as one of the most challenging problems in Semantic Web services (SWS),aims to filter and rank a set of services with respect to a service query by using a certain matching strategy.In this paper,we propose a logistic regression based method to aggregate several matching strategies instead of a fixed integration (e.g.,the weighted sum) for SWS matchmaking.The logistic regression model is trained on training data derived from binary relevance assessments of existing test collections,and then used to predict the probability of relevance between a new pair of query and service according to their matching values obtained from various matching strategies.Services are then ranked according to the probabilities of relevance with respect to each query.Our method is evaluated on two main test collections,SAWSDL-TC2 and Jena Geography Dataset(JGD).Experimental results show that the logistic regression model can effectively predict the relevance between a query and a service,and hence can improve the effectiveness of service matchmaking.

关键词： Semantic Web service matchmaking logistic regression

Adaptive and augmented active anomaly detection on dynamic network traffic streams

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Frontiers of Information Technology & Electronic Engineering 2024年第3期25卷 446-460页

作者： Bin LI Yijie WANG Li CHENG national Key laboratory of parallel and distributed Computing College of ComputerNational University of Defense TechnologyChangsha 410073China College of System Engineering National University of Defense TechnologyChangsha 410073China

Active anomaly detection queries labels of sampled instances and uses them to incrementally update the detection model,and has been widely adopted in detecting network attacks.However,existing methods cannot achieve desirable performance on dynamic network traffic streams because(1)their query strategies cannot sample informative instances to make the detection model adapt to the evolving stream and(2)their model updating relies on limited query instances only and fails to leverage the enormous unlabeled instances on streams.To address these issues,we propose an active tree based model,adaptive and augmented active prior-knowledge forest(A3PF),for anomaly detection on network trafic streams.A prior-knowledge forest is constructed using prior knowledge of network attacks to find feature subspaces that better distinguish network anomalies from normal traffic.On one hand,to make the model adapt to the evolving stream,a novel adaptive query strategy is designed to sample informative instances from two aspects:the changes in dynamic data distribution and the uncertainty of anomalies.On the other hand,based on the similarity of instances in the neighborhood,we devise an augmented update method to generate pseudo labels for the unlabeled neighbors of query instances,which enables usage of the enormous unlabeled instances during model updating.Extensive experiments on two benchmarks,CIC-IDS2017 and UNSW-NB15,demonstrate that A3PF achieves significant improvements over previous active methods in terms of the area under the receiver operating characteristic curve(AUC-ROC)(20.9%and 21.5%)and the area under the precision-recall curve(AUC-PR)(44.6%and 64.1%).

关键词： Active anomaly detection Network traffic streams Pseudo labels Prior knowledge of network attacks

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Survey of DHT topology construction techniques in virtual computing environments

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Science China(Information Sciences) 2011年第11期54卷 2221-2235页

作者： ZHANG YiMing 1,2,LU XiCheng 1,2 & LI DongSheng 1,21 national laboratory for parallel and distributed processing (PDL),Changsha 410073,China 2 School of Computer,national University of Defense Technology,Changsha 410073,China national laboratory for parallel and distributed processing (PDL) Changsha China School of Computer National University of Defense Technology Changsha China

The Internet-based virtual computing environment (iVCE) is a novel network computing platform.The characteristics of growth,autonomy,and diversity of Internet resources present great challenges to resource sharing in iVCE.The DHT overlay (DHT for short) technique has various advantages such as high scalability,low latency,and desirable availability,and is thus an important approach to realizing efficient resource sharing.Topology construction is a key technique for structured overlays that realizes basic overlay functions including dynamic maintenance and message routing.In this paper,we first introduce the traditional techniques of DHT topology construction,focusing mainly on dynamic maintenance and message routing of typical DHTs,DHT indexing techniques for complex queries,and DHT grouping techniques for matching domain structures.We then present recent advances in DHT topology construction techniques in iVCE taking advantage of the characteristics of Internet resources.Finally,we discuss the future of DHT topology construction techniques.

关键词： virtual computing environments DHT overlays topology construction distributed indexing flexible routing

Synergistic enhancement on mechanical properties and corrosion resistance of biodegradable Mg-Zn-Y alloy via V-microalloying

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Journal of Magnesium and Alloys 2024年第2期12卷 530-545页

作者： Jiaxin Zhang Xin Ding Ruirun Chen Wenchao Cao Jinshan Zhang Rui Zhao national Key laboratory for Precision Hot processing of Metals Harbin Institute of TechnologyNo.92West Dazhi StreetHarbinHeilongjiang 150001China College of Materials Science and Engineering Taiyuan University of TechnologyNo.79West Yingze StreetTaiyuanShanxi 030024China

For the sake of improving the mechanical properties and corrosion resistance of biodegradable Mg alloy synergistically,various content of element V(0,0.05,0.10,0.15,0.20 wt.%)are introduced into an Mg-Zn-Y alloy with long-period stacking ordered(LPSO)structure,and the effects of V on its microstructure,mechanical properties and corrosion resistance are investigated systematically.The results indicate that the grains are effectively refined by V addition,and the primaryα-Mg in Mg-Zn-Y-V0.1 alloy is most significantly refined,with grain size being decreased by 62%.The amount of 18R LPSO structure is increased owing to the V addition.The growth mode of the second phase(W-phase and 18R LPSO structure)is transformed to divorced growth pattern,which ascribes to the thermodynamic drive force of V to promote the nucleation of LPSO phase.Thus,18R LPSO structure presents a continuous distribution.Due to grains refinement and modification of second phase,the tensile strength and strain of alloys are both enhanced effectively.Especially,the ultimate tensile strength and the elongation of V0.1 alloy are 254 MPa and 15.26%,which are 41%and 61%higher than those of V-free alloy,respectively.Owing to the continuously distributed 18R LPSO structure with refined grains and stable product film,the weight loss and hydrogen evolution corrosion rates of V0.1 alloy are 7.1 and 6.2 mmy^(-1),respectively,which are 42.6%and 45.4%lower than those of V-free alloy.

关键词： Corrosion Mechanical property V-microalloying LPSO SKPFM

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Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

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International Journal of Minerals,Metallurgy and Materials 2024年第5期31卷 1089-1097页

作者： Jianjun Xu Hanlin Ding Xin Lin Feng Liu Analytical&Testing Center Northwestern Polytechnical UniversityXi’an 710072China State Key laboratory of Solidification processing Northwestern Polytechnical UniversityXi’an 710072China

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

关键词： directed energy deposition Ni-based superalloys high-temperature preheating hot isostatic pressing microstructure tensile properties

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