Towards Scalable Synchronization on Multi-Cores

The shift of commodity hardware from single- to multi-core processors in the early 2000s compelled software developers to take advantage of the available parallelism of multi-cores. Unfortunately, only few---so-called embarrassingly parallel---applications can leverage this available parallelism in a straightforward manner. The remaining---non-embarrassingly parallel---applications require that their processes coordinate their possibly interleaved executions to ensure overall correctness---they require synchronization. Synchronization is achieved by constraining or even prohibiting parallel execution. Thus, per Amdahl's law, synchronization limits software scalability. In this dissertation, we explore how to minimize the effects of synchronization on software scalability. We show that scalability of synchronization is mainly a property of the underlying hardware. This means that synchronization directly hampers the cross-platform performance portability of concurrent software. Nevertheless, we can achieve portability without sacrificing performance, by creating design patterns and abstractions, which implicitly leverage hardware details without exposing them to software developers. We first perform an exhaustive analysis of the performance behavior of synchronization on several modern platforms. This analysis clearly shows that the performance and scalability of synchronization are highly dependent on the characteristics of the underlying platform. We then focus on lock-based synchronization and analyze the energy/performance trade-offs of various waiting techniques. We show that the performance and the energy efficiency of locks go hand in hand on modern x86 multi-cores. This correlation is again due to the characteristics of the hardware that does not provide practical tools for reducing the power consumption of locks without sacrificing throughput. We then propose two approaches for developing portable and scalable concurrent software, hence hiding the limitations that the underlying multi-cores impose. First, we introduce OPTIK, a new practical design pattern for designing and implementing fast and scalable concurrent data structures. We illustrate the power of our OPTIK pattern by devising five new algorithms and by optimizing four state-of-the-art algorithms for linked lists, skip lists, hash tables, and queues. Second, we introduce MCTOP, a multi-core topology abstraction which includes low-level information, such as memory bandwidths. MCTOP enables developers to accurately and portably define high-level optimization policies. We illustrate several such policies through four examples, including automated backoff schemes for locks, and illustrate the performance and portability of these policies on five platforms

Information society and the state: the Greek version of the information society paradigm

The concept of the 'information society' has been systematically deployed to denote a new techno-socio-economic paradigm with information and communication technologies (ICTs) at the centre, which entails significant economic and social transformations and bears implications for governance and potential for development and quality of life. Departing from the deterministic view of information society as a set of uniform societal arrangements, the thesis examines its national variations, as they emerge from the interaction between ICTs and relevant policies with pre-existing social, political and economic realities. Drawing on a conceptual framework based on political economy and historical sociology, it proposes that the unfolding of any national information society is a contested process feeding on the historically formed relationship between the state and the national economy and society. This relationship is expected to inflect international policies and processes in quite idiosyncratic ways, leading to differentiated national information society trajectories, while the state is instrumental in articulating international policy directions with national societal arrangements. Identifying an empirical gap in the examination and analysis in semi-peripheral and middle-income countries, the thesis seeks to address evolving characteristics and dimensions of the 'Greek case' of information society, stressing the dialectic between European policy and the national socio-cultural, political and economic idiosyncrasies, the role of the Greek state, as well as the weaknesses encountered in the process. The emphasis is on the period 1998-2008, which includes the first comprehensive strategy and provides the opportunity to analyse preliminary results of the policies adopted. The empirical material includes relevant policy documents, quantitative indicators, personal observations, as well as a set of elite interviews with policymakers, ICT industry representatives and other actors involved in information society policies and processes