Optimising subdomain aspect ratios for parallel load balancing

In parallel adaptive Finite Element simulations the work load 011the individual processors can change frequently. To (re)distribute the load evenly over the processors a load balancing heuristic is needed. Common strategies try to minimise subdomain dependencies by minimising the number of cut edges in the partition. For many solvers this is the most influential factor. However for example, for certain preconditioned Conjugate Gradient solvers this cutsize can play only a minor role, but their convergence can be highly dependent on the subdomain shapes. Degenerated subdomain shapes can cause them to need significantly more iterations to converge. Common heuristics often fail to address these requirements. In this thesis a new strategy is introduced which directly addresses the problem of generating and conserving reasonably good subdomain shapes while balancing the load in a dynamically changing Finite Element Simulation. A new definition of Aspect Ratio is presented which assesses subdomain shapes. The common methodology of using adjacency information to select the best elements to be migrated is not considered since it is not necessarily related to the subdomain shapes. Instead, geometric data is used to formulate several cost functions to rate elements in terms of their suitability to be migrated. The well known diffusive and Generalised Dimension Exchange methods which calculate the necessary load flow are enhanced by weighting the subdomain edges in order to influence their impact on the resulting partition positively. The results of comprehensive tests are presented and demonstrate that the proposed methods are competitive with state-of-the-art load balancing tools

Structural framework conditions and individual motivations for youth-mobility: A macro-micro level approach for different European country-types

European youth mobility seems to be fostering Europe's unequal pace of integration, which sees certain countries benefit at the expense of others (Ohmacht et al., 2009; van Mol & Timmerman, 2014). Using a comparative approach, the paper aims to relate a macro-level country-typology focussing on human capital with individual mobility-motivations on the micro-level. Our methodological approach is based on a secondary macro-data analysis and analyses of mobility-motivations of young people (micro-data) deriving from qualitative (N=152) and quantitative data (N=5,499) collected in six European countries. In order to examine correspondence between macro-conditions and micro-aspects, we relate information on mobility-motivations to the country-typology by allocating mobile youth to the respective types of their home country. The results show that the country-types compose different opportunity structures, which are reflected in individual motivations. Accordingly, different country-types can be seen as an example of the heterogeneity and inequality of European social and territorial mobility frames

Wie? Warum? Oder warum nicht? Mobilitätsfelder sowie Motivationen und Barrieren für Jugendmobilität in Europa

Auslandserfahrungen sind nicht nur eine Möglichkeit, auf kulturelle Entdeckungsreise zu gehen. Sie gelten auch als Chance für junge Menschen, zu lernen und sich persönlich und beruflich weiterzuentwickeln. Entsprechend wird Jugendmobilität in der Jugendarbeit große Aufmerksamkeit geschenkt. Auch die Länder, die die Jugendlichen entsenden oder aufnehmen, können dabei profitieren – aber auf unterschiedliche Weise. Zu welchem Zweck gehen junge Menschen ins Ausland? Was motiviert sie dabei? Welche Barrieren müssen sie dafür überwinden? Welche Rolle spielt der familiäre Bildungshintergrund der Jugendlichen? Diese Fragen werden mit Fokus auf länderspezifische Unterschiede auf der Datenbasis des europäischen Forschungsprojekts MOVE untersucht, in das Wissenschaftler(innen) aus sechs europäischen Ländern involviert waren. Die Grundlage bildet zunächst eine Ländertypologie, die Humankapitalbewegungen durch Auslandsaufenthalte abbildet, welche je nach Mobilitätsfeld eher dem Sende- oder Empfängerland zugutekommen. Sie weist europäische Länder vier Typen zu: Mobilitätsförderern, Mobilitätsverlierern, Mobilitätsgewinnern und Mobilitätsverwertern. Besonders erstere und letztere sind gut für eine kontrastierende, ländervergleichende Betrachtung geeignet. Mobilitätsförderer sind Länder, deren junge Menschen im europäischen Ausland arbeiten, die aber selbst kein wichtiges Zielland für europäische Jugendliche sind (z.B. Ungarn und Rumänien). Mobilitätsverwerter sind attraktive Zielländer sowohl für kurz- als auch langfristige Mobilitäten und weisen damit bezüglich der Generierung und Verwertung von Humankapital ein ausgeglichenes Konto auf (z.B. Norwegen, Luxemburg und Deutschland). In einem kontrastierenden Vergleich werden Motivationen und Barrieren für Auslandsaufenthalte im Zusammenhang mit dem Bildungshintergrund junger Menschen aus Mobilitätsförder- und Mobilitätsverwerterländern analysiert. Hierfür werden die Individualdaten eines Onlinesurveys mit 18-29-Jährigen (N=4.719) aus Deutschland, Luxemburg, Norwegen, Ungarn und Rumänien den beiden Ländertypen zugeordnet und verglichen

Quality balancing for parallel adaptive FEM

We present a dynamic distributed load balancing algorithm for parallel, adaptive finite element simulations using preconditioned conjugate gradient solvers based on domain-decomposition. The load balancer is designed to maintain good partition aspect ratios. It can calculate a balancing flow using different versions of diffusion and a variant of breadth first search. Elements to be migrated are chosen according to a cost function aiming at the optimization of subdomain shapes. We show how to use information from the second step to guide the first. Experimental results using Bramble's preconditioner and comparisons to existing state-ot-the-art load balancers show the benefits of the construction

Aspect ratio for mesh partitioning

This paper deals with the measure of Aspect Ratio for mesh partitioning and gives hints why, for certain solvers, the Aspect Ratio of partitions plays an important role. We define and rate different kinds of Aspect Ratio, present a new center-based partitioning method which optimizes this measure implicitly and rate several existing partitioning methods and tools under the criterion of Aspect Ratio

Capturing and Composing Parallel Patterns with Intel CnC

The most accessible and successful parallel tools today are those that ask programmers to write only isolated serial kernels, hiding parallelism behind a library interface. Examples include Google’s Map-Reduce [5], CUDA [13], and STAPL [12]. This encapsulation approach applies to a wide range of structured, well-understood algorithms, which we call parallel patterns. Today’s highlevel systems tend to encapsulate only a single pattern. Thus we explore the use of Intel CnC as a single framework for capturing and composing multiple patterns.

A Performance Monitoring Interface for OpenMP

Abstract. This paper reports on efforts to define a performance monitoring interface for OpenMP that merges the OMPI and POMP prototype interfaces developed in the past year. The primary goal is to define a clear and portable API for OpenMP that makes execution events visible to runtime monitoring tools, primarily tools for performance measurement. The proposed specification is presented, covering many relevant design issues and the result of discussions among the involved groups. Both successful convergence of ideas, leading to agreement on proposed specifications, as well as differences in opinion and remaining open issues are documented from our many discussions. The paper is intended to serve as a preliminary proposal for consideration by the OpenMP Architecture Review Board and recently formed Tools sub-committee.

The Concurrent Collections Programming Model

We introduce the Concurrent Collections (CnC) programming model. In this model, programs are written in terms of high-level operations. These operations are partially ordered according to only their semantic constraints. These partial orderings correspond to data dependences and control dependences. The role of the domain expert, whose interest and expertise is in the application domain, and the role of the tuning expert, whose interest and expertise is in performance on a specific architecture, can be viewed as separate concerns. The CnC programming model pro vides a high-level specification that can be used as a common language between the two experts, raising the level of their discourse. The model facilitates a significant degree of separation, which simplifies the task of the domain expert, who can focus on the application rather than scheduling concerns and mapping to the target architecture. This separation also simplifies the work of the tuning expert, who is given the maximum possible freedom to map the computation onto the target architecture and is not required to understand the details of the domain. However, the domain and tuning expert may still be the same person. We formally describe the execution semantics of CnC and prove that this model guarantees deterministic computation. We evaluate the performance of CnC implementations on several applications and show that CnC can effectively exploit several different kinds of parallelism and offer performance and scalability that is equivalent to or better than that offered by the current low-level parallel programming models. Further, with respect to ease of programming, we discuss the tradeoffs between CnC and other parallel program ming models on these applications