A survey on architectures and energy efficiency in Data Center Networks

Data Center Networks (DCNs) are attracting growing interest from both academia and industry to keep pace with the exponential growth in cloud computing and enterprise networks. Modern DCNs are facing two main challenges of scalability and cost-effectiveness. The architecture of a DCN directly impacts on its scalability, while its cost is largely driven by its power consumption. In this paper, we conduct a detailed survey of the most recent advances and research activities in DCNs, with a special focus on the architectural evolution of DCNs and their energy efficiency. The paper provides a qualitative categorization of existing DCN architectures into switch-centric and server-centric topologies as well as their design technologies. Energy efficiency in data centers is discussed in details with survey of existing techniques in energy savings, green data centers and renewable energy approaches. Finally, we outline potential future research directions in DCNs

Next Steps for Human-Centered Generative AI: A Technical Perspective

Through iterative, cross-disciplinary discussions, we define and propose next-steps for Human-centered Generative AI (HGAI) from a technical perspective. We contribute a roadmap that lays out future directions of Generative AI spanning three levels: Aligning with human values; Accommodating humans' expression of intents; and Augmenting humans' abilities in a collaborative workflow. This roadmap intends to draw interdisciplinary research teams to a comprehensive list of emergent ideas in HGAI, identifying their interested topics while maintaining a coherent big picture of the future work landscape

Ranking Viscous Finger Simulations to an Acquired Ground Truth with Topology-aware Matchings

International audienceThis application paper presents a novel framework based on topological data analysis for the automatic evaluation and ranking of viscous finger simulation runs in an ensemble with respect to a reference acquisition. Individual fingers in a given time-step are associated with critical point pairs in the distance field to the injection point, forming persistence diagrams. Different metrics, based on optimal transport, for comparing time-varying persistence diagrams in this specific applicative case are introduced. We evaluate the relevance of the rankings obtained with these metrics, both qualitatively thanks to a lightweight web visual interface, and quantitatively by studying the deviation from a reference ranking suggested by experts. Extensive experiments show the quantitative superiority of our approach compared to traditional alternatives. Our web interface allows experts to conveniently explore the produced rankings. We show a complete viscous fingering case study demonstrating the utility of our approach in the context of porous media fluid flow, where our framework can be used to automatically discard physically-irrelevant simulation runs from the ensemble and rank the most plausible ones. We document an in-situ implementation to lighten I/O and performance constraints arising in the context of parametric studies

Intermediador de serviços na Nuvem

Mestrado em Engenharia de Computadores e TelemáticaDe acordo com história dos sistemas informáticos, os engenheiros têm vindo a remodelar infraestruturas para melhorar a eficiência das organizações, visando o acesso partilhado a recursos computacionais. O advento da computação em núvem desencadeou um novo paradigma, proporcionando melhorias no alojamento e entrega de serviços através da Internet. Quando comparado com abordagens tradicionais, este apresenta vantajens por disponibilizar acesso ubíquo, escalável e sob demanda, a determinados conjuntos de recursos computacionais partilhados. Ao longo dos últimos anos, observou-se a entrada de novos operadores que providenciam serviços na núvem, a preços competitivos e diferentes acordos de nível de serviço (“Service Level Agreements”). Com a adoção crescente e sem precedentes da computação em núvem, os fornecedores da área estão se a focar na criação e na disponibilização de novos serviços, com valor acrescentado para os seus clientes. A competitividade do mercado e a existência de inúmeras opções de serviços e de modelos de negócio gerou entropia. Por terem sido criadas diferentes terminologias para conceitos com o mesmo significado e o facto de existir incompatibilidade de Interfaces de Programação Aplicacional (“Application Programming Interface”), deu-se uma restrição de fornecedores de serviços específicos na núvem a utilizadores. A fragmentação na faturação e na cobrança ocorreu quando os serviços na núvem passaram a ser contratualizados com diferentes fornecedores. Posto isto, seria uma mais valia existir uma entidade, que harmonizasse a relação entre os clientes e os múltiplos fornecedores de serviços na núvem, por meio de recomendação e auxílio na intermediação. Esta dissertação propõe e implementa um Intermediador de Serviços na Núvem focado no auxílio e motivação de programadores para recorrerem às suas aplicações na núvem. Descrevendo as aplicações de modo facilitado, um algoritmo inteligente recomendará várias ofertas de serviços na núvem cumprindo com os requisitos aplicacionais. Desta forma, é prestado aos utilizadores formas de submissão, gestão, monitorização e migração das suas aplicações numa núvem de núvens. A interação decorre a partir de uma única interface de programação que orquestrará todo um processo juntamente com outros gestores de serviços na núvem. Os utilizadores podem ainda interagir com o Intermediador de Serviços na Núvem a partir de um portal Web, uma interface de linha de comandos e bibliotecas cliente.Throughout the history of computer systems, experts have been reshaping IT infrastructure for improving the efficiency of organizations by enabling shared access to computational resources. The advent of cloud computing has sparked a new paradigm providing better hosting and service delivery over the Internet. It offers advantages over traditional solutions by providing ubiquitous, scalable and on-demand access to shared pools of computational resources. Over the course of these last years, we have seen new market players offering cloud services at competitive prices and different Service Level Agreements. With the unprecedented increasing adoption of cloud computing, cloud providers are on the look out for the creation and offering of new and valueadded services towards their customers. Market competitiveness, numerous service options and business models led to gradual entropy. Mismatching cloud terminology got introduced and incompatible APIs locked-in users to specific cloud service providers. Billing and charging become fragmented when consuming cloud services from multiple vendors. An entity recommending cloud providers and acting as an intermediary between the cloud consumer and providers would harmonize this interaction. This dissertation proposes and implements a Cloud Service Broker focusing on assisting and encouraging developers for running their applications on the cloud. Developers can easily describe their applications, where an intelligent algorithm will be able to recommend cloud offerings that better suit application requirements. In this way, users are aided in deploying, managing, monitoring and migrating their applications in a cloud of clouds. A single API is required for orchestrating the whole process in tandem with truly decoupled cloud managers. Users can also interact with the Cloud Service Broker through a Web portal, a command-line interface, and client libraries

Cross-Layer Pathfinding for Off-Chip Interconnects

Off-chip interconnects for integrated circuits (ICs) today induce a diverse design space, spanning many different applications that require transmission of data at various bandwidths, latencies and link lengths. Off-chip interconnect design solutions are also variously sensitive to system performance, power and cost metrics, while also having a strong impact on these metrics. The costs associated with off-chip interconnects include die area, package (PKG) and printed circuit board (PCB) area, technology and bill of materials (BOM). Choices made regarding off-chip interconnects are fundamental to product definition, architecture, design implementation and technology enablement. Given their cross-layer impact, it is imperative that a cross-layer approach be employed to architect and analyze off-chip interconnects up front, so that a top-down design flow can comprehend the cross-layer impacts and correctly assess the system performance, power and cost tradeoffs for off-chip interconnects. Chip architects are not exposed to all the tradeoffs at the physical and circuit implementation or technology layers, and often lack the tools to accurately assess off-chip interconnects. Furthermore, the collaterals needed for a detailed analysis are often lacking when the chip is architected; these include circuit design and layout, PKG and PCB layout, and physical floorplan and implementation. To address the need for a framework that enables architects to assess the system-level impact of off-chip interconnects, this thesis presents power-area-timing (PAT) models for off-chip interconnects, optimization and planning tools with the appropriate abstraction using these PAT models, and die/PKG/PCB co-design methods that help expose the off-chip interconnect cross-layer metrics to the die/PKG/PCB design flows. Together, these models, tools and methods enable cross-layer optimization that allows for a top-down definition and exploration of the design space and helps converge on the correct off-chip interconnect implementation and technology choice. The tools presented cover off-chip memory interfaces for mobile and server products, silicon photonic interfaces, 2.5D silicon interposers and 3D through-silicon vias (TSVs). The goal of the cross-layer framework is to assess the key metrics of the interconnect (such as timing, latency, active/idle/sleep power, and area/cost) at an appropriate level of abstraction by being able to do this across layers of the design flow. In additional to signal interconnect, this thesis also explores the need for such cross-layer pathfinding for power distribution networks (PDN), where the system-on-chip (SoC) floorplan and pinmap must be optimized before the collateral layouts for PDN analysis are ready. Altogether, the developed cross-layer pathfinding methodology for off-chip interconnects enables more rapid and thorough exploration of a vast design space of off-chip parallel and serial links, inter-die and inter-chiplet links and silicon photonics. Such exploration will pave the way for off-chip interconnect technology enablement that is optimized for system needs. The basis of the framework can be extended to cover other interconnect technology as well, since it fundamentally relates to system-level metrics that are common to all off-chip interconnects