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  • 301.
    Keller, Jörg
    et al.
    FernUniversität in Hagen, Germany.
    Majeed, Mudassar
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Balancing CPU Load for Irregular MPI Applications2012Ingår i: Advances in Parallel Computing: Applications, Tools and Techniques on the Road to Exascale Computing / [ed] Koen De Bosschere, Erik H. D'Hollander, Gerhard R. Joubert, David Padua, Frans Peters, Mark Sawyer, IOS Press, 2012, 307-316 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    MPI applications typically are designed to be run on a parallel machine with one process per core. If processes exhibit different computational load, either the code must be rewritten for load balancing, with negative side-effects on readability and maintainability, or the one-process-per-core philosophy leads to a low utilization of many processor cores. If several processes are mapped per core to increase CPU utilization, the load might still be unevenly distributed among the cores if the mapping is unaware of the process characteristics.

    Therefore, similarly to the MPI_Graph_create() function where the program gives hints on communication patterns so that MPI processes can be placed favorably, we propose a MPI_Load_create() function where the program supplies information on the relative loads of the MPI processes, such that processes can be favorably grouped and mapped onto processor cores. In order to account for scalability and restricted knowledge of individual MPI processes, we also propose an extension MPI_Dist_load_create() similar to MPI_Dist_graph_create(), where each individual MPI process only knows the loads of a subset of the MPI processes.

    We detail how to implement both variants on top of MPI, and provide experimental performance results both for synthetic and numeric example applications. The results indicate that load balancing is favorable in both cases.

  • 302.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Compiling for VLIW DSPs2013Ingår i: Handbook of signal processing systems / [ed] Shuvra S. Bhattacharyya, Ed F. Deprettere, Rainer Leupers, Jarmo Takala, New York: Springer, 2013, 2, 1177-1214 s.Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This handbook, organized into four parts, provides the reader with a comprehensive and standalone overview of signal processing systems. It contains a comprehensive index for ease of use, and an extensive bibliography for further reading.

  • 303.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Compiling for VLIW DSPs2010Ingår i: Handbook of signal processing systems / [ed] Shuvra S. Bhattacharyya, Ed F. Deprettere, Rainer Leupers, Jarmo Takala, New York: Springer, 2010, 1, 603-638 s.Kapitel i bok, del av antologi (Refereegranskat)
  • 304.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Fourth Swedish Workshop on Multi-Core Computing MCC-2011: November 23-25, 2011, Linköping University, Linköping, Sweden2011Proceedings (redaktörskap) (Övrigt vetenskapligt)
    Abstract [en]

    MCC-2011 covers a wide variety of topics, including programming for GPU-based systems, mobile multi-core based platforms, scalable concurrent data structures, memory hierarchies, auto-tuning, transactional memory and thread-level speculation, parallel programming models, scheduling and mapping, applications, and even teaching of multicore programming.

  • 305.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Programming Techniques for the Cell Processor2011Ingår i: it - Information Technology, ISSN 1611-2776, Vol. 53, nr 2, 66-74 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cell Broadband Engine is a heterogeneous multicore processor designed mainly for applications in scientific computing, graphics, and gaming with high performance requirements. We give an overview of its architecture, review some selected development tools and programming frameworks, and describe techniques for writing efficient programs for Cell.

  • 306.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Programming the Cell Processor2010Ingår i: Fundamentals of Multicore Software Development / [ed] Victor Pankratius, Ali-Reza Adl-Tabatabai, Walter Tichy, CRC Press, 2010, 155-198 s.Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 307.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Li, Lu
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Optimized Composition: Generating Efficient Code for Heterogeneous Systems from Multi-Variant Components, Skeletons and Containers2014Ingår i: Proc. First Workshop on Resource awareness and adaptivity in multi-core computing (Racing 2014), May 2014, Paderborn, Germany / [ed] F. Hannig and J. Teich, 2014, 43-48 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this survey paper, we review recent work on frameworks for the high-level, portable programming of heterogeneous multi-/manycore systems (especially, GPU-based systems) using high-level constructs such as annotated user-level software components, skeletons (i.e., predefined generic components) and containers, and discuss the optimization problems that need to be considered in selecting among multiple implementation variants, generating code and providing runtime support for efficient execution on such systems.

  • 308.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Majeed, Mudassar
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Furmento, Nathalie
    University of Bordeaux, INRIA, Bordeaux, France.
    Thibault, Samuel
    University of Bordeaux, INRIA, Bordeaux, France.
    Namyst, Raymond
    University of Bordeaux, INRIA, Bordeaux, France.
    Benkner, Siegfried
    University of Vienna, Austria.
    Pllana, Sabri
    University of Vienna, Austria.
    Träff, Jesper
    Technical University of Vienna, Austria.
    Wimmer, Martin
    Technical University of Vienna, Austria.
    Leveraging PEPPHER Technology for Performance Portable Supercomputing2013Ingår i: High Performance Computing, Networking, Storage and Analysis (SCC), 2012 SC Companion, Salt Lake City, USA: IEEE conference proceedings, 2013, 1395-1396 s.Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    PEPPHER is a 3-year EU FP7 project that develops a novel approach and framework to enhance performance portability and programmability of heterogeneous multi-core systems. Its primary target is single-node heterogeneous systems, where several CPU cores are supported by accelerators such as GPUs. This poster briefly surveys the PEPPHER framework for single-node systems, and elaborates on the prospectives for leveraging the PEPPHER approach to generate performance-portable code for heterogeneous multi-node systems.

  • 309.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Thibault, Samuel
    INRIA / University of Bordeaux, France.
    Namyst, Raymond
    INRIA / University of Bordeaux, France.
    Richards, Andrew
    Codeplay Software Ltd., Edinburgh, UK.
    Dolinsky, Uwe
    Codeplay Software Ltd., Edinburgh, UK.
    Benkner, Siegfried
    University of Vienna, Austria.
    Träff, Jesper
    Technical University of Vienna, Austria.
    Pllana, Sabri
    University of Vienna, Austria.
    Programmability and Performance Portability Aspects of Heterogeneous Multi-/Manycore Systems2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    We discuss three complementary approaches that can provide both portability and an increased level of abstraction for the programming of heterogeneous multicore systems. Together, these approaches also support performance portability, as currently investigated in the EU FP7 project PEPPHER. In particular, we consider (1) a library-based approach, here represented by the integration of the SkePU C++ skeleton programming library with the StarPU runtime system for dynamic scheduling and dynamic selection of suitable execution units for parallel tasks; (2) a language-based approach, here represented by the Offload-C++ high-level language extensions and Offload compiler to generate platform-specific code; and (3) a component-based approach, specifically the PEPPHER component system for annotating user-level application components with performance metadata, thereby preparing them for performance-aware composition. We discuss the strengths and weaknesses of these approaches and show how they could complement each other in an integrational programming framework for heterogeneous multicore systems.

  • 310.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eitschberger, Patrick
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Energy-Efficient Static Scheduling of Streaming Task Collections with Malleable Tasks2013Ingår i: Proc. 25th PARS-Workshop, Gesellschaft für Informatik, 2013, 37-46 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the energy-efficiency of streaming task collections with parallelizable or malleable tasks on a manycore processor with frequency scaling. Streaming task collections differ from classical task sets in that all tasks are running concurrently, so that cores typically run several tasks that are scheduled round-robin on user level. A stream of data flows through the tasks and intermediate results are forwarded to other tasks like in a pipelined task graph. We first show the equivalence of task mapping for streaming task collections and normal task collections in the case of continuous frequency scaling, under reasonable assumptions for the user-level scheduler, if a makespan, i.e. a throughput requirement of the streaming application, is given and the energy consumed is to be minimized. We then show that in the case of discrete  frequency scaling, it might be necessary for processors to switch frequencies, and that idle times still can occur, in contrast to continuous frequency scaling. We formulate the mapping of (streaming) task collections on a manycore processor with discrete frequency levels as an integer linear program. Finally, we propose two heuristics to reduce energy consumption compared to the previous results by improved load balancing through the parallel execution of a parallelizable task. We evaluate the effects of the heuristics analytically and experimentally on the Intel SCC.

  • 311.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Hansson, Erik
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Flexible scheduling and thread allocation for synchronous parallel tasks2012Ingår i: ARCS-2012 Workshops / [ed] G. Mühl, J. Richling, A. Herkersdorf, Gesellschaft für Informatik , 2012, 517-528 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    We describe a task model and dynamic scheduling and resource allocation mechanism for synchronous parallel tasks to be executed on SPMD-programmed synchronous shared memory MIMD parallel architectures with uniform, unit-time memory access and strict memory consistency, also known inthe literature as PRAMs (Parallel Random Access Machines). Our task model provides a two-tier programming model for PRAMs that flexibly combines SPMD and fork-join parallelism within the same application. It offers flexibility by dynamic scheduling and late resource binding while preserving the PRAM execution properties within each task, the only limitation being that the maximum number of threads that can be assigned to a task is limited to what the underlying architecture provides. In particular, our approach opens for automatic performance tuning at run-time by controlling the thread allocation for tasks based on run-time predictions.By a prototype implementation of a synchronous parallel task API in the SPMD-based PRAM language Fork and experimental evaluation with example programs on the SBPRAM simulator, we show that a realization of the task model on a SPMD-programmable PRAM machine is feasible with moderate runtimeoverhead per task.

  • 312.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Li, Lu
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Atalar, Aras
    Chalmers University of Technology, Gothenburg, Sweden.
    Dobre, Alin
    Movidius, Dublin, Ireland.
    XPDL: Extensible Platform Description Language to Support Energy Modeling and Optimization2015Ingår i: Proc. 44th International Conference on Parallel Processing Workshops, ICPP-EMS Embedded Multicore Systems, in conjunction with ICPP-2015, Beijing, 1-4 sep. 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, 51-60 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present XPDL, a modular, extensible platform description language for heterogeneous multicore systems and clusters. XPDL specifications provide platform metadata about hardware and installed system software that are relevant for the adaptive static and dynamic optimization of application programs and system settings for improved performance and energy efficiency. XPDL is based on XML and uses hyperlinks to create distributed libraries of platform metadata specifications. We also provide first components of a retarget able tool chain that browses and processes XPDL specifications, and generates driver code for micro benchmarking to bootstrap empirical performance and energy models at deployment time. A C++ based API enables convenient introspection of platform models, even at run-time, which allows for adaptive dynamic program optimizations such as tuned selection of implementation variants.

  • 313.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Melot, Nicolas
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eitschberger, Patrick
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Crown Scheduling: Energy-Efficient Resource Allocation, Mapping and Discrete Frequency Scaling for Collections of Malleable Streaming Tasks2013Ingår i: Proceedings of the 23rd International Workshop on Power and Timing Modeling, Optimization and Simulation (PATMOS), 2013 / [ed] Jörg Henkel and Alex Yakovlev (eds.), IEEE Computer Society Digital Library, 2013, 215-222 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the problem of generating energy-optimal code for a collection of streaming tasks that include parallelizable or malleable tasks on a generic many-core processor with dynamic discrete frequency scaling. Streaming task collections differ from classical task sets in that all tasks are running concurrently, so that cores typically run several tasks that are scheduled round-robin at user level in a data driven way. A stream of data flows through the tasks and intermediate results are forwarded to other tasks like in a pipelined task graph. In this paper we present crown scheduling, a novel technique for the combined optimization of resource allocation, mapping and discrete voltage/frequency scaling for malleable streaming task sets in order to optimize energy efficiency given a throughput constraint. We present optimal off-line algorithms for separate and integrated crown scheduling based on integer linear programming (ILP). We also propose extensions for dynamic rescaling to automatically adapt a given crown schedule in situations where not all tasks are data ready. Our energy model considers both static idle power and dynamic power consumption of the processor cores. Our experimental evaluation of the ILP models for a generic manycore architecture shows that at least for small and medium sized task sets even the integrated variant of crown scheduling can be solved to optimality by a state-of-the-art ILP solver within a few seconds.

  • 314.
    Kessler, Christoph
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Pllana, SabriLinnaeus University, Växjö.
    Proceedings of the 2013 IEEE 6th International Workshop on Multi-/Many-core Computing Systems (MuCoCoS-2013)2013Proceedings (redaktörskap) (Refereegranskat)
  • 315.
    Kessler, Martin
    et al.
    Linköpings universitet.
    Hansson, Erik
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Åkesson, Daniel
    Linköpings universitet, Institutionen för datavetenskap. Linköpings universitet, Tekniska högskolan.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Exploiting Instruction Level Parallelism for REPLICA - A Configurable VLIW Architecture With Chained Functional Units2012Ingår i: : Volume II, Las Vegas, Nevada, USA: CSREA Press, 2012, 275-281 s.Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In this paper we present a scheduling algorithm for VLIW architectures with chained functional units. We show how our algorithm can help speed up programs at the instruction level, for an architecture called REPLICA, a configurable emulated shared memory (CESM) architecture whose computation model is based on the PRAM model. Since our LLVM based compiler is parameterizable in the number of different functional units, read and write ports to register file etc. we can generate code for different REPLICA architectures that have different functional unit configurations. We show for a set of different configurations how our implementation can produce high quality code; and we argue that the high parametrization of the compiler makes it, together with the simulator, useful for hardware/software co-design.

  • 316.
    Kim, Jin-Hyun
    et al.
    INRIA/IRISA, France.
    Legay, Axel
    INRIA/IRISA, France.
    Traonouez, Louis-Marie
    INRIA/IRISA, France.
    Boudjadar, Abdeldjalil
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Nyman, Ulrik
    Aalborg University, Denmark.
    Larsen, Kim G.
    Aalborg University, Denmark.
    Lee, Insup
    University of Pennsylvania.
    Choi, Jin-Young
    Korea University, S. Korea.
    Optimizing the Resource Requirements of Hierarchical Scheduling Systems2016Ingår i: SIGBED Review, ISSN 1551-3688, Vol. 13, nr 3, 41-48 s.Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Compositional reasoning on hierarchical scheduling systems is a well-founded formal method that can construct schedulable and optimal system configurations in a compositional way. However, a compositional framework formulates the resource requirement of a component, called an interface, by assuming that a resource is always supplied by the parent components in the most pessimistic way. For this reason, the component interface demands more resources than the amount of resources that are really sufficient to satisfy sub-components. We provide two new supply bound functions which provides tighter bounds on the resource requirements of individual components. The tighter bounds are calculated by using more information about the scheduling system.

    We evaluate our new tighter bounds by using a model-based schedulability framework for hierarchical scheduling systems realized as Uppaal models. The timed models are checked using model checking tools Uppaal and Uppaal SMC, and we compare our results with the state of the art tool CARTS.

  • 317.
    Kinnander, Åke
    et al.
    Siemens Turbo Machinery AB, Finspång, Sweden.
    Sjölund, Martin
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Pop, Adrian
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Industrial Evaluation of Integrated Performance Analysis and Equation Model Debugging for Equation-Based Models2016Ingår i: Modeling, Identification and Control, ISSN 0332-7353, E-ISSN 1890-1328, Vol. 37, nr 4, 225-236 s., 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ease of use and the high abstraction level of equation-based object-oriented (EOO) languages such as Modelica has the drawback that performance problems and modeling errors are often hard to find. To address this problem, we have earlier developed advanced performance analysis and equation model debugging support in the OpenModelica tool. The aim of the work reported in this paper is to perform an independent investigation and evaluation of this equation model performance analysis and debugging methods and tool support on industrial models. The results turned out to be mainly positive. The integrated debugger and performance analyzer locates several kinds of errors such as division by zero, chattering, etc., and greatly facilitates finding the equations that take most of the execution time during simulation. It remains to further evaluate the performance profiler and debugger on even larger industrial models.

  • 318.
    Kosuch, Stefanie
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Approximability of the two-stage stochastic knapsack problem with discretely distributed weights2014Ingår i: Discrete Applied Mathematics, ISSN 0166-218X, E-ISSN 1872-6771, Vol. 165, 192-204 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper the two-stage knapsack problem with random weights is studied under the aspect of approximability. We assume finite probability distributions for the weights and show that, unless P = NP, the so obtained problem cannot be approximated in polynomial time within a better ratio than K-1/2 (where K is the number of second-stage scenarios). We further study the special cases where in the second stage items can only be added or only be removed, but not both. Positive approximation results are given for three particular cases, namely linearly dependent first- and second-stage rewards, the polynomial scenario model and the case where the number of scenarios is assumed to be a constant. To the best of our knowledge, this is the first study of a two-stage knapsack problem under the aspect of approximability and the first time a non-approximability result has been proven for a stochastic knapsack problem of any kind.

  • 319.
    Krispinsson, Tobias
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Hybrid application development: A comparison between native Android application and Ionic 2 application2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis, the newly released framework Ionic 2, which claims to fix the problems cross platform frameworks has suffered from concerning bad performance and bad user experience, has been evaluated. The study has focused on the Android platform by comparing a native developed application to an Ionic 2 developed application. The comparison has been made on performance and user experience. As an extent, Ionic 2 are also compared to another evaluation study made for React Native, to see how the two frameworks differ, both performance wise and user experience wise. The native application performs better in all performance tests, even though the difference only was a few percent for memory usage and battery consumption. In the user tests, the result was of different nature. Some users did not notice any differences between the applications, whilst some had big concerns with how the application behaved. The overall conclusion is that Ionic still has some way to go to compete with native applications. If considering using Ionic 2, you need to be aware of the flaws it has. From the data gathered for this study, React Native is considered to be better than Ionic, but with new updates coming continuously, Ionic is improving every day.

  • 320.
    Kuhlmann, Marco
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Interaktiva och kognitiva system. Linköpings universitet, Tekniska fakulteten.
    Jonsson, Peter
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Parsing to Noncrossing Dependency Graphs2015Ingår i: Transactions of the Association for Computational Linguistics, ISSN 2307-387X, Vol. 3, 559-570 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the generalization of maximum spanning tree dependency parsing to maximum acyclic subgraphs. Because the underlying optimization problem is intractable even under an arc-factored model, we consider the restriction to noncrossing dependency graphs. Our main contribution is a cubic-time exact inference algorithm for this class. We extend this algorithm into a practical parser and evaluate its performance on four linguistic data sets used in semantic dependency parsing. We also explore a generalization of our parsing framework to dependency graphs with pagenumber at most $k$ and show that the resulting optimization problem is NP-hard for k ≥ 2.

  • 321.
    Kuiper, Erik
    et al.
    Saab Aeronautical, Linkoping, Sweden .
    Nadjm-Tehrani, Simin
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Yuan, Di
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
    A framework for performance analysis of geographic delay-tolerant routing2012Ingår i: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, nr 184Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A major tool used for evaluating routing protocols in ad hoc and delay-tolerant networks is simulation. Whereas the results from simulations give good insights, they are limited to the specific scenario set-up that is used. If the scenario changes, new and often time-consuming simulations have to be run. Moreover, the simulation time in packet-level simulators with fairly realistic physical layer implementation, such as ns-2, generally grows rapidly in the number of nodes. This practically limits the number of nodes in a simulation, even if the limit can be extended by the use of simulation federations. Larger scenarios can also be facilitated by the use of more abstraction in the physical layer; abstractions that may impact the validity of the results. In this article, we present the forward-wait framework--a mathematical model describing the packet movements for opportunistic geographic delay-tolerant routing protocols. By describing packet movements as a sequence of alternating forwarding and waiting phases, the framework can accurately predict the routing performance. Key input parameters to the framework are random variables describing the forwarding and waiting phases. We show how the properties of the random variables can be derived, both via abstract modeling and small scale ns-2 simulation data. The model is then used to demonstrate the prediction capabilities of the framework in providing results that are close to the (much slower) packet-level simulations.

  • 322.
    Kurin, Erik
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Melin, Adam
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Data-driven test automation: augmenting GUI testing in a web application2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    For many companies today, it is highly valuable to collect and analyse data in order to support decision making and functions of various sorts. However, this kind of data-driven approach is seldomly applied to software testing and there is often a lack of verification that the testing performed is relevant to how the system under test is used. Therefore, the aim of this thesis is to investigate the possibility of introducing a data-driven approach to test automation by extracting user behaviour data and curating it to form input for testing.

    A prestudy was initially conducted in order to collect and assess different data sources for augmenting the testing. After suitable data sources were identified, the required data, including data about user activity in the system, was extracted. This data was then processed and three prototypes where built on top of this data. The first prototype augments the model-based testing by automatically creating models of the most common user behaviour by utilising data mining algorithms. The second prototype tests the most frequent occurring client actions. The last prototype visualises which features of the system are not covered by automated regression testing.

    The data extracted and analysed in this thesis facilitates the understanding of the behaviour of the users in the system under test. The three prototypes implemented with this data as their foundation can be used to assist other testing methods by visualising test coverage and executing regression tests.

  • 323.
    Kvarnström, Olle
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Static Code Analysis of C++ in LLVM2016Självständigt arbete på grundnivå (kandidatexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Just like the release of the Clang compiler, the advent of LLVM in the field of static code analysis already shows great promise. When given the task of covering rules not ideally covered by a commercial contender, the end result is not only overwhelmingly positive, the implementation time is only a fraction of what was initially expected. While LLVM’s support for sophisticated AST analysis is remarkable, being the main reason these positive results, it’s support for data flow analysis is not yet up to par. Despite this, as well as a lack of thorough documentation, LLVM should already be a strong rival for any commercial tool today.

  • 324.
    Lagerberg, Lina
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Skude, Tor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    The impact of agile principles and practices on large-scale software development projects: A multiple-case study of two software development projects at Ericsson2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Agile software development methods are often advertised as a contrast to the traditional, plan-driven approach to software development. The reported and argued benefits on software quality, coordination, productivity and other areas are numerous. The base of empirical evidence to the claimed effects is however thin, and more empirical studies on the effects of agile software development methods in different contexts are needed, especially in large-scale, industrial settings.

    The purpose of the thesis was to study the impact of using agile principles and practices in large-scale software development projects at Ericsson and it was carried out as a multiple-case study of two projects. One of the projects had implemented a limited number of agile software development practices and was largely plan-driven, while the other project had fully adapted its organization and product design for agile software development. Propositions of possible effects of the use of agile principles and practices in the two projects were generated by a literature review. Empirical data was then collected from online surveys of project members, internal documents, personal contact with key project members and a collection of metrics, to study the presence of the proposed effects.

    The study was focused on eight different areas: internal software documentation, knowledge sharing, project visibility, pressure and stress, productivity, software quality and project success rate.

    Agile principles and practices were found to:

    • Lead to a more balanced use of internal software documentation, when supported by sound documentation policies.
    • Contribute to knowledge sharing.
    • Increase project members’ visibility of the status of other teams and the entire project.
    • Increase coordination effectiveness and reducing the need for other types of coordination mechanisms.
    • Increase productivity.
    • Possibly increase software quality.

    Additionally, the study showed that internal software documentation is important also in agile software development projects, and cannot fully be replaced with face-to-face communication. Further, it was clear that it’s possible to make a partial implementation of agile principles and practices, and still receive a positive impact. Finally, the study showed that it’s feasible to implement agile principles and practices in large-scale software development. It therefore contributes to understanding the effects of agile software development in different contexts.

  • 325.
    Lagerberg, Lina
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Skude, Tor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Sandahl, Kristian
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Emanuelsson, Pär
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Ståhl, Daniel
    Ericsson AB, Linköping, Sweden.
    The impact of agile principles and practices on large-scale software development projects: A multiple-case study of two projects at Ericsson2013Ingår i: Empirical Software Engineering and Measurement, 2013, Los Alamitos: IEEE , 2013, 348-356 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    BACKGROUND: Agile software development methods have a number of reported benefits on productivity, project visibility, software quality and other areas. There are also negative effects reported. However, the base of empirical evidence to the claimed effects needs more empirical studies. AIM: The purpose of the research was to contribute with empirical evidence on the impact of using agile principles and practices in large-scale, industrial software development. Research was focused on impacts within seven areas: Internal software documentation, Knowledge sharing, Project visibility, Pressure and stress, Coordination effectiveness, and Productivity. METHOD: Research was carried out as a multiple-case study on two contemporary, large-scale software development projects with different levels of agile adoption at Ericsson. Empirical data was collected through a survey of project members. RESULTS AND CONCLUSIONS: Intentional implementation of agile principles and practices were found to: correlate with a more balanced use of internal software documentation, contribute to knowledge sharing, correlate with increased project visibility and coordination effectiveness, reduce the need for other types of coordination mechanisms, and possibly increase productivity. No correlation with increase in pressure and stress were found.

  • 326.
    Lagerkvist, Vicktor
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Wahlström, Magnus
    Department of Computer Science, Royal Holloway, University of London, Great Britain.
    Zanuttini, Bruno
    GREYC, Normandie Université, UNICAEN, CNRS, ENSICAEN, Franc.
    Bounded Bases of Strong Partial Clones2015Ingår i: Multiple-Valued Logic (ISMVL), 2015 IEEE International Symposium on, IEEE , 2015, 189-194 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    Partial clone theory has successfully been applied to study the complexity of the constraint satisfaction problem parameterized by a set of relations (CSP(G)). Lagerkvist & Wahlstroï¿œm (ISMVL 2014) however shows that the partial polymorphisms of G (?P?I(G)) cannot be finitely generated for finite, Boolean G if CSP(G) is NP-hard (assuming P?NP). In this paper we consider stronger closure operators than functional composition which can generate ?P?I(G) from a finite set of partial functions, a bounded base. Determining bounded bases for finite languages provides a complete characterization of their partial polymorphisms and we provide such bases for k-SAT and 1-in-k-SAT.

  • 327.
    Lagerkvist, Victor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Precise Upper and Lower Bounds for the Monotone Constraint Satisfaction Problem2015Ingår i: MATHEMATICAL FOUNDATIONS OF COMPUTER SCIENCE 2015, PT I, SPRINGER-VERLAG BERLIN , 2015, Vol. 9234, 357-368 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    The monotone constraint satisfaction problem (MCSP) is the problem of, given an existentially quantified positive formula, decide whether this formula has a model. This problem is a natural generalization of the constraint satisfaction problem, which can be seen as the problem of determining whether a conjunctive formula has a model. In this paper we study the worst-case time complexity, measured with respect to the number of variables, n, of the MCSP problem parameterized by a constraint language Gamma (MCSP(Gamma)). We prove that the complexity of the NP-complete MCSP(G) problems on a given finite domain D falls into exactly vertical bar D vertical bar-1 cases and ranges from O(2(n)) to O(vertical bar D vertical bar(n)). We give strong lower bounds and prove that MCSP(G), for any constraint language Gamma over any finite domain, is solvable in O(vertical bar Dvertical bar n) time, where D- is the domain of the core of Gamma, but not solvable in O(vertical bar Dvertical bar(delta n)) time for any delta < 1, unless the strong exponential-time hypothesis fails. Hence, we obtain a complete understanding of the worst-case time complexity of MCSP(Gamma) for constraint languages over arbitrary finite domains.

  • 328.
    Lagerkvist, Victor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Strong Partial Clones and the Complexity of Constraint Satisfaction Problems: Limitations and Applications2016Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis we study the worst-case time complexity of the constraint satisfaction problem parameterized by a constraint language (CSP(S)), which is the problem of determining whether a conjunctive formula over S has a model. To study the complexity of CSP(S) we borrow methods from universal algebra. In particular, we consider algebras of partial functions, called strong partial clones. This algebraic approach allows us to obtain a more nuanced view of the complexity CSP(S) than possible with algebras of total functions, clones.

    The results of this thesis is split into two main parts. In the first part we investigate properties of strong partial clones, beginning with a classification of weak bases for all Boolean relational clones. Weak bases are constraint languages where the corresponding strong partial clones in a certain sense are extraordinarily large, and they provide a rich amount of information regarding the complexity of the corresponding CSP problems. We then proceed by classifying the Boolean relational clones according to whether it is possible to represent every relation by a conjunctive, logical formula over the weak base without needing more than a polynomial number of existentially quantified variables. A relational clone satisfying this condition is called polynomially closed and we show that this property has a close relationship with the concept of few subpowers. Using this classification we prove that a strong partial clone is of infinite order if (1) the total functions in the strong partial clone are essentially unary and (2) the corresponding constraint language is finite. Despite this, we prove that these strong partial clones can be succinctly represented with finite sets of partial functions, bounded bases, by considering stronger notions of closure than functional composition.

    In the second part of this thesis we apply the theory developed in the first part. We begin by studying the complexity of CSP(S) where S is a Boolean constraint language, the generalised satisfiability problem (SAT(S)). Using weak bases we prove that there exists a relation R such that SAT({R}) is the easiest NP-complete SAT(S) problem. We rule out the possibility that SAT({R}) is solvable in subexponential time unless a well-known complexity theoretical conjecture, the exponential-time hypothesis, (ETH) is false. We then proceed to study the computational complexity of two optimisation variants of the SAT(S) problem: the maximum ones problem over a Boolean constraint language S (MAX-ONES(S)) and the valued constraint satisfaction problem over a set of Boolean cost functions Δ (VCSP(Δ)). For MAX-ONES(S) we use partial clone theory and prove that MAX-ONES({R}) is the easiest NP-complete MAX-ONES(S) problem. These algebraic techniques do not work for VCSP(Δ), however, where we instead use multimorphisms to prove that MAX-CUT is the easiest NP-complete Boolean VCSP(Δ) problem. Similar to the case of SAT(S) we then rule out the possibility of subexponential algorithms for these problems, unless the ETH is false.

  • 329.
    Lagerkvist, Victor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Weak bases of Boolean co-clones2014Ingår i: Information Processing Letters, ISSN 0020-0190, E-ISSN 1872-6119, Vol. 114, nr 9, 462-468 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Universal algebra has proven to be a useful tool in the study of constraint satisfaction problems (CSP) since the complexity, up to logspace reductions, is determined by the clone of the constraint language. But two CSPs corresponding to the same clone may still differ substantially with respect to worst-case time complexity, which makes clones ill-suited when comparing running times of CSP problems. In this article we instead consider an algebra where each clone splits into an interval of strong partial clones such that a strong partial clone corresponds to the CSPs that are solvable within the same O(c(n)) bound. We investigate these intervals and give relational descriptions, weak bases; of the largest elements. They have a highly regular form and are in many cases easily relatable to the smallest members in the intervals, which suggests that the lattice of strong partial clones has a simpler structure than the lattice of partial clones.

  • 330.
    Lagerkvist, Victor
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Wahlström, Magnus
    Linköpings universitet, Institutionen för datavetenskap, TCSLAB - Laboratoriet för teoretisk datalogi. Linköpings universitet, Tekniska högskolan. Univ London, Dept Comp Sci, London WC1E 7HU, England.
    Polynomially Closed Co-clones2014Ingår i: 2014 IEEE 44TH INTERNATIONAL SYMPOSIUM ON MULTIPLE-VALUED LOGIC (ISMVL 2014), IEEE Computer Society, 2014, 85-90 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    Two well-studied closure operators for relations are based on primitive positive (p.p.) definitions and quantifier free p.p. definitions. The latter do however have limited expressiveness and the corresponding lattice of strong partial clones is uncountable. We consider implementations allowing polynomially many existentially quantified variables and obtain a dichotomy for co-clones where such implementations are enough to implement any relation and prove (1) that all remaining coclones contain relations requiring a superpolynomial amount of quantified variables and (2) that the strong partial clones corresponding to two of these co-clones are of infinite order whenever the set of invariant relations can be finitely generated.

  • 331.
    Lagerkvist, Victor
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Wahlström, Magnus
    Royal Holloway University of London, England.
    The power of primitive positive definitions with polynomially many variables2017Ingår i: Journal of logic and computation (Print), ISSN 0955-792X, E-ISSN 1465-363X, Vol. 27, nr 5, 1465-1488 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two well-studied closure operators for relations are based on existentially quantified conjunctive formulas, primitive positive (p.p.) definitions, and primitive positive formulas without existential quantification, quantifier-free primitive positive definitions (q.f.p.p.) definitions. Sets of relations closed under p.p. definitions are known as co-clones and sets of relations closed under q.f.p.p. definitions as weak partial co-clones. The latter do however have limited expressivity, and the corresponding lattice of strong partial clones is of uncountably infinite cardinality even for the Boolean domain. Hence, it is reasonable to consider the expressiveness of p.p. definitions where only a small number of existentially quantified variables are allowed. In this article, we consider p.p. definitions allowing only polynomially many existentially quantified variables, and say that a co-clone closed under such definitions is polynomially closed, and otherwise superpolynomially closed. We investigate properties of polynomially closed co-clones and prove that if the corresponding clone contains a k-ary near-unanimity operation for k amp;gt;= 3, then the co-clone is polynomially closed, and if the clone does not contain a k-edge operation for any k amp;gt;= 2, then the co-clone is superpolynomially closed. For the Boolean domain we strengthen these results and prove a complete dichotomy theorem separating polynomially closed co-clones from superpolynomially closed co-clones. Using these results, we then proceed to investigate properties of strong partial clones corresponding to superpolynomially closed co-clones. We prove that if Gamma is a finite set of relations over an arbitrary finite domain such that the clone corresponding to Gamma is essentially unary, then the strong partial clone corresponding to Gamma is of infinite order and cannot be generated by a finite set of partial functions.

  • 332.
    Lambrix, Patrick
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Göthe Lundgren, Maud
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
    Kamkar, Mariam
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Computer science as an integrated part of engineering education1997Ingår i: Proceedings of the ACM SIGCSE/SIGCUE Conference on Integrating Technology into Computer Science Education, 1997, 151- s.Konferensbidrag (Refereegranskat)
  • 333.
    Lambrix, Patrick
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Kamkar, Mariam
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Computer Science as an Integrated Part of Engineering Education1998Ingår i: Proceedings of the Third ACM SIGCSE/SIGCUE Conference on Integrating Technology into Computer Science Education, 1998, 153-156 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Information Technology curriculum at Linköping University has as goal to form engineers with an integrated view of engineering. The teaching philosophy in this curriculum is Problem-Based Learning. The education in each term is organised in a number of themes where topics from different disciplines are integrated. We describe a particular term in the Information Technology curriculum as an example of the approach and the integration of computer science teaching with the teaching of other disciplines. An important advantage of the approach is that the students discover interactions between different disciplines and view the different topics as naturally connected. Also, the students seem to have a better understanding of the topics and are better motivated. Further, they obtain improved communication and co-operation skills. Another advantage is that the approach is appreciated by our female students, which has led to a higher percentage of female students in this curriculum compared to our other computer science curricula.

  • 334.
    Larsson, Adam
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Prestandautvärdering av koppling mellan C#.NET och Pitch Runtime Infrastructure2014Självständigt arbete på grundnivå (högskoleexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna rapport dokumenterar arbetet med att utreda hur C# och Pitch RTI fungerar tillsammans, och vilka prestandaeffekter som resulterar av denna koppling. Motiveringen kommer från att kunder till företaget Pitch har efterfrågat stöd för C# som programmeringsspråk när de använder Pitch RTI. Metoden gick ut på att successivt lära sig använda de tekniker som finns tillgängliga, för att sedan implementera lösningar på hur kopplingen ska ske. Resultaten visar hur övergången går till och prestandan som uppnåddes med hjälp av indexnotation. Tekniken IKVM hade högre prestandaindex och gick snabbare att komma igång med jämfört med tekniken C++/CLI. Men C++/CLI passar bättre ur ett distributionsperspektiv. Slutsatsen blev att Pitch som företag med hjälp av denna rapport är bättre förberett på framtida utredningar och implementationer som skulle använda de utvärderade teknikerna.

  • 335.
    Larsson, Christian
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Application development for automated positioning of 3D-representations of a modularized product2013Självständigt arbete på grundnivå (högskoleexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta examensarbete presenterar en applikation som positionerar moduler automatiskt med hjälp av given data för varje modul, samt utvecklingen av applikationen. Applikationen bygger på kod från ett tidigare examensarbete. Ovanpå den koden har flera egenskaper och felhanteringar lagts till, samt har olika buggar fixats. Ett stresstest har också utförts och framtida utvecklingsmöjligheter presenteras.

    Examensarbetet genomfördes på Toyota Material Handling Mjölby (TMH) och gjordes parallellt med ett annat examensarbete av Fredrik Holden som genererade data för applikationen. För en fullständig förståelse angående teorin bakom samt bakgrunden till examensarbetet, vänligen läs också Holdens rapport ”Developmentof method  for automated positioning of 3D-representations of a modularized product”, samt rapporten från föregeånde examensarbetet ”Analysis for Automated Positioning of 3D-representation of a Modularized product”.

  • 336.
    Laurentz, Henrik
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Feasibility of using network support data to predict risk level of trouble tickets2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Internet Service Providers gather vast amounts of data in the form of trouble tickets created from connectivity related issues. This data is often stored and seldom used for proactive purposes. This thesis explores the feasibility of finding correlations in network support data through the use of data mining activities. Correlations such as these could be used for improving troubleshooting or staffing related activities. The approach uses the data mining methodology CRISP-DM to investigate typical data mining operations from the perspective of a Network Operation Center. The results show that correlations between the solving time and other ticket related attributes do exist and that support data could be used for the activities mentioned. The results also show that it exists a lot of room for improvement when it comes to data mining activities in network support data.

  • 337.
    Lewin, Marcus
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Grant, Harald
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Klientbaserad GeoTIFF-rendering2017Självständigt arbete på grundnivå (kandidatexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    När en användare idag efterfrågar rendering av en kartvy i en applikation behöver en server först rendera en bild utifrån given geografisk data och därefter skicka bilden till klientens mobila enhet. Detta kan resultera i höga responstider, speciellt för användare som befinner sig i områden med bristfällig täckning. I denna studie utvärderas en alternativ lösning där rendering istället sker direkt på klientens enhet. En prototyp av en mobil kartapplikation med stöd för lokal rendering av geografisk rådata utvecklas och utvärderas utefter en konstant för acceptabel fördröjning vid visualisering av information. Resultatet av testerna visar att prototypens prestanda är beroende av mängden information som ska visas. För högre zoomnivåer ger prototypen ett tillfredsställande resultat, men vidare åtgärder krävs för de lägre nivåerna. De främsta utmaningarna vid utvecklingen av applikationen redovisas och förbättringsförslag för fortsatt utveckling framförs.

  • 338.
    Li, James Jizhi
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Requirement Verification in Modelica For a Small Scale Network Simulation2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The usage of computer networks has increased enormously recently due to many benefits; it facilitates data distribution speed, long distance communication and industrial system control. Due to these reasons, industry systems have started to use computer networks for system control and data transmission. Meanwhile, the limitations of network devices also raise many challenges for network system configuration. To have the best optimized network system, we need to study the network system by performing experiments. However, experiments on the real systems could be expensive and dangerous. Therefore, we need a model to represent the behaviours of the system.

    This thesis work uses object-oriented acasual modelling language Modelica to model a local area network system, and the development is performed in OpenModelica, an open source Modelica-based modelling and simulation environment. The simulation results are analysed and verified by using a separate requirement verification model.

  • 339.
    Li, Lu
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Adaptive Off-Line Tuning for Optimized Composition of Components for Heterogeneous Many-Core Systems2013Ingår i: High Performance Computing for Computational Science - VECPAR 2012, Springer, 2013, 329-345 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    In recent years heterogeneous multi-core systems have been given much attention. However, performance optimization on these platforms remains a big challenge. Optimizations performed by compilers are often limited due to lack of dynamic information and run time environment, which makes applications often not performance portable. One current approach is to provide multiple implementations for the same interface that could be used interchangeably depending on the call context, and expose the composition choices to a compiler, deployment-time composition tool and/or run-time system. Using off-line machine-learning techniques allows to improve the precision and reduce the run-time overhead of run-time composition and leads to an improvement of performance portability. In this work we extend the run-time composition mechanism in the PEPPHER composition tool by off-line composition and present an adaptive machine learning algorithm for generating compact and efficient dispatch data structures with low training time. As dispatch data structure we propose an adaptive decision tree structure, which implies an adaptive training algorithm that allows to control the trade-off between training time, dispatch precision and run-time dispatch overhead.

    We have evaluated our optimization strategy with simple kernels (matrix-multiplication and sorting) as well as applications from RODINIA benchmark on two GPU-based heterogeneous systems. On average, the precision for composition choices reaches 83.6 percent with approximately 34 minutes off-line training time.

  • 340.
    Li, Lu
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Pruning strategies in adaptive off-line tuning for optimized composition of components on heterogeneous systems2014Ingår i: 2014 43rd International Conference on Parallel Processing Workshops (ICCPW), IEEE conference proceedings, 2014, 255-264 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    Adaptive program optimizations, such as automatic selection of the expected fastest implementation variant for a computation component depending on runtime context, are important especially for heterogeneous computing systems but require good performance models. Empirical performance models based on trial executions which require no or little human efforts show more practical feasibility if the sampling and training cost can be reduced to a reasonable level. In previous work we proposed an early version of adaptive pruning algorithm for efficient selection of training samples, a decision-tree based method for representing, predicting and selecting the fastest implementation variants for given run-time call context properties, and a composition tool for building the overall composed application from its components. For adaptive pruning we use a heuristic convexity assumption. In this paper we consolidate and improve the method by new pruning techniques to better support the convexity assumption and better control the trade-off between sampling time, prediction accuracy and runtime prediction overhead. Our results show that the training time can be reduced by up to 39 times without noticeable prediction accuracy decrease. Furthermore, we evaluate the effect of combinations of pruning strategies and compare our adaptive sampling method with random sampling. We also use our smart-sampling method as a preprocessor to a state-of-the-art decision tree learning algorithm and compare the result to the predictor directly calculated by our method.

  • 341.
    Li, Lu
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Dastgeer, Usman
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Pruning strategies in adaptive off-line tuning for optimized composition of components on heterogeneous systems2016Ingår i: Parallel Computing, ISSN 0167-8191, E-ISSN 1872-7336, Vol. 51, 37-45 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adaptive program optimizations, such as automatic selection of the expected fastest implementation variant for a computation component depending on hardware architecture and runtime context, are important especially for heterogeneous computing systems but require good performance models. Empirical performance models which require no or little human efforts show more practical feasibility if the sampling and training cost can be reduced to a reasonable level. In previous work we proposed an early version of adaptive sampling for efficient exploration and selection of training samples, which yields a decision-tree based method for representing, predicting and selecting the fastest implementation variants for given run-time call contexts property values. For adaptive pruning we use a heuristic convexity assumption. In this paper we consolidate and improve the method by new pruning techniques to better support the convexity assumption and control the trade-off between sampling time, prediction accuracy and runtime prediction overhead. Our results show that the training time can be reduced by up to 39 times without noticeable prediction accuracy decrease. (C) 2015 Elsevier B.V. All rights reserved.

  • 342.
    Li, Lu
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Kessler, Christoph
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    MeterPU: A Generic Measurement Abstraction API Enabling Energy-tuned Skeleton Backend Selection2015Ingår i: Trustcom/BigDataSE/ISPA, 2015 IEEE, IEEE Press, 2015, Vol. 3, 154-159 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present MeterPU, an easy-to-use, generic and low-overhead abstraction API for taking measurements of various metrics (time, energy) on different hardware components (e.g. CPU, DRAM, GPU), using pluggable platform-specific measurement implementations behind a common interface in C++. We show that with MeterPU, not only legacy (time) optimization frameworks, such as autotuned skeleton back-end selection, can be easily retargeted for energy optimization, but also switching different optimization goals for arbitrary code sections now becomes trivial. We apply MeterPU to implement the first energytunable skeleton programming framework, based on the SkePU skeleton programming library.

  • 343.
    Lianjie, Shen
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Optimization and Search in Model-Based Automotive SW/HW Development2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis two case studies are performed about solving two design problems we face during the design phase of new Volvo truck. One is to solve the frame packing problem on CAN bus. The other is to solve the LDC allocation problem. Both solutions are targeted to meet as many end-to-end latency requirements as possible. Now the solution is obtained through manually approach and based on the designer experience. But it is still not satisfactory enough. With the development of artificial intelligence method we propose two methods based on genetic algorithm to solve our design problem we face today. In first case study about frame packing we perform one single genetic algorithm process to find the optimal solution. In second case study about LDC allocation we proposed how to handle two genetic algorithm processes together to reach the optimal solution. In this thesis we show the feasibility of adopting artificial intelligence concept in some activities of the truck design phases like we do in both case studies.  

  • 344.
    Lifa, Adrian Alin
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Hardware/Software Codesign of Embedded Systems with Reconfigurable and Heterogeneous Platforms2015Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Modern applications running on today's embedded systems have very high requirements. Most often, these requirements have many dimensions: the applications need high performance as well as exibility, energy-eciency as well as real-time properties, fault tolerance as well as low cost. In order to meet these demands, the industry is adopting architectures that are more and more heterogeneous and that have reconguration capabilities. Unfortunately, this adds to the complexity of designing streamlined applications that can leverage the advantages of such architectures.

    In this context, it is very important to have appropriate tools and design methodologies for the optimization of such systems. This thesis addresses the topic of hardware/software codesign and optimization of adaptive real-time systems implemented on recongurable and heterogeneous platforms. We focus on performance enhancement for dynamically recongurable FPGA-based systems, energy minimization in multi-mode real-time systems implemented on heterogeneous platforms, and codesign techniques for fault-tolerant systems.

    The solutions proposed in this thesis have been validated by extensive experiments, ranging from computer simulations to proof of concept implementations on real-life platforms. The results have conrmed the importance of the addressed aspects and the applicability of our techniques for design optimization of modern embedded systems.

  • 345.
    Lifa, Adrian Alin
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Context-Aware Speculative Prefetch for Soft Real-Time Applications2012Ingår i: International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2012), Seoul, Korea, August 19-22, 2012, IEEE, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamically reconfigurable computing devices have the ability to adapt their hardware to application demands, providing the performance of hardware acceleration, as well as high flexibility, at competitive costs. For these reasons, FPGA-based reconfigurable systems are becoming popular in many application domains, including soft real-time computing. Unfortunately, one of their biggest limitations is the high reconfiguration overhead. One method to overcome this problem is configuration prefetching, which tries to reduce the reconfiguration penalty by preloading modules on the FPGA before they are needed, and overlapping the reconfiguration with useful computation. In this paper we present a speculative approach to context-aware inter-procedural configuration prefetching that provides statistical guarantees by minimizing the alpha-percentile of the execution time distribution of a soft real-time application. Our method uses profile information and takes into account the calling context of a procedure in order to generate better prefetch solutions. We also propose a middleware needed to apply the context-dependent prefetches at run-time. Our experiments show that the developed algorithm outperforms the previous state-of-art.

  • 346.
    Lifa, Adrian Alin
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Dynamic Configuration Prefetching Based on Piecewise Linear Prediction2013Ingår i: Design, Automation & Test in Europe (DATE 2013), IEEE , 2013, 815-820 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    Modern systems demand high performance, as well as high degrees of flexibility and adaptability. Many current applications exhibit a dynamic and nonstationary behavior, having certain characteristics in one phase of their execution, that will change as the applications enter new phases, in a manner unpredictable at design-time. In order to meet the performance requirements of such systems, it is important to have on-line optimization algorithms, coupled with adaptive hardware platforms, that together can adjust to the run-time conditions. We propose an optimization technique that minimizes the expected execution time of an application by dynamically scheduling hardware prefetches. We use a piecewise linear predictor in order to capture correlations and predict the hardware modules to be reached. Experiments show that the proposed algorithm outperforms the previous state-of-art in reducing the expected execution time by up to 27% on average.

  • 347.
    Lifa, Adrian Alin
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Execution Time Minimization Based on Hardware/Software Partitioning and Speculative Prefetch2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report addresses the problem of minimizing the average execution time of an application, based on speculative FPGA configuration prefetch. Dynamically reconfigurable systems (like FPGAs) provide both the performance of hardware acceleration and the flexibility and adaptability that modern applications require. Unfortunately, one of their main drawbacks that significantly impacts performance is the high reconfiguration overhead. Configuration prefetching is one method to reduce this penalty by overlapping FPGA reconfigurations with useful computations. In order to make it effective and to avoid very high misprediction penalties, it is important to prefetch the configurations that provide the highest performance improvement, and to do this early enough to hide the reconfiguration overhead. In this report we propose a speculative approach that schedules prefetches at design time and simultaneously performs HW/SW partitioning, in order to minimize the expected execution time of an application. Our method prefetches and executes in hardware those configurations that provide the highest performance improvement. The algorithm takes into consideration profiling information (such as branch probabilities and execution time distributions), correlated with the application characteristics. We demonstrate the effectiveness of our approach compared to the previous state-of-art using extensive experiments, including real-life case studies.

  • 348.
    Lifa, Adrian Alin
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska högskolan.
    Minimization of Average Execution Time Based on Speculative FPGA Configuration Prefetch2012Ingår i: International Conference on ReConFigurable Computing and FPGAs, 2012, IEEE, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the main drawbacks that significantly impacts the performance of dynamically reconfigurable systems (like FPGAs), is their high reconfiguration overhead. Configuration prefetching is one method to reduce this penalty by overlapping FPGA reconfigurations with useful computations. In this paper we propose a speculative approach that schedules prefetches at design time and simultaneously performs HW/SW partitioning, in order to minimize the expected execution time of an application. Our method prefetches and executes in hardware those configurations that provide the highest performance improvement. The algorithm takes into consideration profiling information (such as branch probabilities and execution time distributions), correlated with the application characteristics. Compared to the previous state-of-art, we reduce the reconfiguration penalty with 34% on average, and with up to 59% for particular case studies.

  • 349.
    Lifa, Adrian
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    A Reconfigurable Framework for Performance Enhancement with Dynamic FPGA Configuration Prefetching2016Ingår i: IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, ISSN 0278-0070, E-ISSN 1937-4151, Vol. 35, nr 1, 100-113 s.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many modern applications exhibit a dynamic and nonstationary behavior, with certain characteristics in one phase of their execution, which change as the application enters new phases, in a manner unpredictable at design-time. In order to meet the demands of such applications, it is important to have adaptive and self-reconfiguring hardware platforms, coupled with intelligent on-line optimization algorithms, that together can adjust to the run-time requirements. Partially dynamically reconfigurable field programmable gate array architectures offer both high performance and flexibility. Despite these potential advantages, the challenges faced by designers trying to set-up a functioning system are still significant, mainly because of the still immature design tools and limited device drivers. We propose a complete framework, based on Xilinx’s commercial design suite, that enables an application designer to leverage the advantages of partial dynamic reconfiguration with minimal effort. Our IP-based architecture, together with the comprehensive application programming interface, can be employed to accelerate an application by dynamically scheduling hardware prefetches. Moreover, a piecewise linear predictor is used to capture correlations and predict the hardware modules that will generate the highest performance improvement. Our evaluation comprises of extensive simulations, as well as a complete implementation of the smallest univalue segment assimilating nucleus image processing application on the ML605 board from Xilinx. The measurements show a significant reduction of the expected execution time compared to previous state-of-the-art prefetching algorithms, with only a minor energy overhead.

  • 350.
    Lifa, Adrian
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Eles, Petru
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    Peng, Zebo
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    On-the-fly Energy Minimization for Multi-Mode Real-Time Systems on Heterogeneous Platforms2015Ingår i: 2015 13th IEEE Symposium on Embedded Systems For Real-time Multimedia (ESTIMedia), IEEE , 2015, 75-84 s.Konferensbidrag (Refereegranskat)
    Abstract [en]

    The increasing computational demands of next generation multimedia systems require innovative optimization methods. Modern heterogeneous architectures bring together multiple general-purpose CPUs and multiple GPUs and FPGAs, in an attempt to answer the performance, energy-efficiency and flexibility requirements of today???s complex multimedia applications. However, in order to leverage the advantages of such architectures, careful optimization is essential. In modern systems, more and more multimedia applications need real-time support (e.g. automotive systems that use image processing for active safety features). Real-time multi-mode systems are a good model for a wide range of applications that dynamically change their computational requirements over time. In this context, intelligent on-line resource management is needed, such that the heterogeneous resources are used in an energy-efficient manner, while meeting the real-time constraints. This paper proposes a resource manager that implements run-time policies to decide on-the-fly task admission and the mapping of active tasks to resources, such that the energy consumption of the system is minimized and all task deadlines are met.

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