Siegfried Benkner

On the collective network of ionic liquid/water mixtures. I. Orientational structure

In this work, the collective structure of aqueous solutions of ionic liquids was studied by means of molecular dynamics simulations. Various concentrations of 1-butyl-3-methyl-imidazolium tetrafluoroborate and TIP3P water were simulated at the very same size of the simulation box. For the analysis, the ternary system cation/anion/water was subdivided into binary networks. The local structure of each of these six networks is investigated by atom-atom radial distribution functions as well as by the so-called g coefficients, which reveal the mutual orientation of the network constituting partners. Furthermore, the collective structure of the whole samples was characterized by the contribution of each species to the static dielectric constant epsilon(omega=0) and to the Kirkwood G(K) factor. The combination of the analysis tools mentioned above provides knowledge about the cross-linking of the ionic species with the dipolar water. Thereby, the interplay between charge-charge and hydrogen bond networks is analyzed in detail.

PEPPHER: Efficient and Productive Usage of Hybrid Computing Systems

PEPPHER, a three-year European FP7 project, addresses efficient utilization of hybrid (heterogeneous) computer systems consisting of multicore CPUs with GPU-type accelerators. This article outlines the PEPPHER performance-aware component model, performance prediction means, runtime system, and other aspects of the project. A larger example demonstrates performance portability with the PEPPHER approach across hybrid systems with one to four GPUs.

QoS support for time-critical grid workflow applications

Time critical grid applications as for example simulations for medical surgery or disaster recovery have special quality of service requirements. The Vienna Grid Environment, developed and evaluated in the context of the EU Project GEMSS, facilitates the provision of HPC applications as QoS-aware grid services by providing support for dynamic negotiation of various QoS guarantees like required execution time and price. In this paper, we extend the QoS mechanisms offered by the Vienna Grid Environment to workflow applications. We describe QoS extensions of the business process execution language and present a first prototype of a corresponding QoS-aware workflow engine which implements different strategies in order to bind the tasks of a workflow to adequate grid services subject to user-specified QoS constraints. We present different grid workflow planning approaches as well as first experimental results

VFCc The Vienna Fortran Compiler

High Performance Fortran (HPF) offers an attractive high-level language interface for programming scalable parallel architectures providing the user with directives for the specification of data distribution and delegating to the compiler the task of generating an explicitly parallel program. Available HPF compilers can handle regular codes quite efficiently, but dramatic performance losses may be encountered for applications which are based on highly irregular, dynamically changing data structures and access patterns. In this paper we introduce the Vienna Fortran Compiler (VFC), a new source-to-source parallelization system for HPF+, an optimized version of HPF, which addresses the requirements of irregular applications. In addition to extended data distribution and work distribution mechanisms, HPF+ provides the user with language features for specifying certain information that decisively influence a program’s performance. This comprises data locality assertions, non-local access specifications and the possibility of reusing runtime-generated communication schedules of irregular loops. Performance measurements of kernels from advanced applications demonstrate that with a high-level data parallel language such as HPF+ a performance close to hand-written message-passing programs can be achieved even for highly irregular codes.

VGE - a service-oriented grid environment for on-demand supercomputing

In this paper, we present the Vienna Grid Environment, a service-oriented grid infrastructure based on standard Web services technologies. VGE automates the provision of HPC applications as grid services for on-demand super-computing and simplifies the construction of client-side applications. As a key distinguishing feature, VGE supports a flexible QoS negotiation model which enables clients to negotiate dynamically, and on a case-by-case basis, QoS guarantees on execution time and price with potential service providers. The VGE service provision framework is currently utilized in the context of the EU Project GEMSS, which focuses on the provision of advanced medical simulation services by means of a grid infrastructure.

AutoTune: a plugin-driven approach to the automatic tuning of parallel applications

Performance analysis and tuning is an important step in programming multicore- and manycore-based parallel architectures. While there are several tools to help developers analyze application performance, no tool provides recommendations about how to tune the code. The AutoTune project is extending Periscope, an automatic distributed performance analysis tool developed by Technische Universitat Munchen, with plugins for performance and energy efficiency tuning. The resulting Periscope Tuning Framework will be able to tune serial and parallel codes for multicore and manycore architectures and return tuning recommendations that can be integrated into the production version of the code. The whole tuning process --- both performance analysis and tuning --- will be performed automatically during a single run of the application.

Vienna Fortran 90

Vienna Fortran 90 is a language extension of Fortran 90 which enables the user to write programs for distributed memory multiprocessors using global data references only. Performance of software on such systems is profoundly influenced by the manner in which data is distributed to the processors. Hence, Vienna Fortran 90 provides the user with a wide range of facilities for the mapping of data to processors. It combines the advantages of the shared memory programming paradigm with mechanisms for explicit user control of those aspects of the program which have the greatest impact on efficiency. The paper presents the major features of Vienna Fortran 90 and gives examples of their use.<<ETX>>

A Cooperative and Adaptive Variable Neighborhood Search for the Multi Depot Vehicle Routing Problem with Time Windows

In this paper we propose two cooperation schemes to compose new parallel variants of the Variable Neighborhood Search (VNS). On the one hand, a coarse-grained cooperation scheme is introduced which is well suited for being enhanced with a solution warehouse to store and manage the so far best found solutions and a self-adapting mechanism for the most important search parameters. This makes an a priori parameter tuning obsolete. On the other hand, a fine-grained scheme was designed to reproduce the successful properties of the sequential VNS. In combination with the use of parallel exploration threads all of the best solutions and 11 out of 20 new best solutions for the Multi Depot Vehicle Routing Problem with Time Windows were found.

Programmability and performance portability aspects of heterogeneous multi-/manycore systems

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.

Towards an Intelligent Environment for Programming Multi-core Computing Systems

In this position paper we argue that an intelligent program development environment that proactively supports the user helps a mainstream programmer to overcome the difficulties of programming multi-core computing systems. We propose a programming environment based on intelligent software agents that enables users to work at a high level of abstraction while automating low-level implementation activities. The programming environment supports program composition in a model-driven development fashion using parallel building blocks and proactively assists the user during major phases of program development and performance tuning. We highlight the potential benefits of using such a programming environment with usage-scenarios. An experiment with a parallel building block on a Sun UltraSPARC T2 Plus processor shows how the system may assist the programmer in achieving performance improvements.