201 research outputs found

    On the role of performance interference in consolidated environments

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    Cotutela Universitat Politècnica de Catalunya i KTH Royal Institute of TechnologyWith the advent of resource shared environments such as the Cloud, virtualization has become the de facto standard for server consolidation. While consolidation improves utilization, it causes performance-interference between Virtual Machines (VMs) from contention in shared resources such as CPU, Last Level Cache (LLC) and memory bandwidth. Over-provisioning resources for performance sensitive applications can guarantee Quality of Service (QoS), however, it results in low machine utilization. Thus, assuring QoS for performance sensitive applications while allowing co-location has been a challenging problem. In this thesis, we identify ways to mitigate performance interference without undue over-provisioning and also point out the need to model and account for performance interference to improve the reliability and accuracy of elastic scaling. The end goal of this research is to leverage on the observations to provide efficient resource management that is both performance and cost aware. Our main contributions are threefold; first, we improve the overall machine utilization by executing best-e↵ort applications along side latency critical applications without violating its performance requirements. Our solution is able to dynamically adapt and leverage on the changing workload/phase behaviour to execute best-e↵ort applications without causing excessive interference on performance; second, we identify that certain performance metrics used for elastic scaling decisions may become unreliable if performance interference is unaccounted. By modelling performance interference, we show that these performance metrics become reliable in a multi-tenant environment; and third, we identify and demonstrate the impact of interference on the accuracy of elastic scaling and propose a solution to significantly minimise performance violations at a reduced cost.Con la aparición de entornos con recurso compartidos tales como la nube, la virtualización se ha convertido en el estándar de facto para la consolidación de servidores. Mientras que la consolidación mejora la utilización, también causa interferencia en el rendimiento de las máquinas virtuales (VM) debido a la contención en recursos compartidos, tales como CPU, el último nivel de cache (LLC) y el ancho de banda de memoria. El exceso de aprovisionamiento de recursos para aplicaciones sensibles al rendimiento puede garantizar la calidad de servicio (QoS), sin embargo, resulta en una baja utilización de la maquina. Por lo tanto, asegurar QoS en aplicaciones sensibles al rendimiento, al tiempo que permitir la co-localización ha sido un problema difícil. En esta tesis, se identifican las formas de mitigar la interferencia sin necesidad de sobre-aprovisionamiento y también se señala la necesidad de modelar y contabilizar la interferencia en el desempeño para mejorar la fiabilidad y la precisión del escalado elástico. El objetivo final de esta investigación consiste en aprovechar las observaciones para proporcionar una gestión eficiente de los recursos considerando tanto el rendimiento como el coste. Nuestras contribuciones principales son tres; primero, mejoramos la utilización total de la maquina mediante la ejecución de aplicaciones best-effort junto con aplicaciones críticas en latencia sin vulnerar sus requisitos de rendimiento. Nuestra solución es capaz de adaptarse de forma dinámica y sacar provecho del comportamiento cambiante de la carga de trabajo y sus cambios de fase para ejecutar aplicaciones best-effort, sin causar interferencia excesiva en el rendimiento; segundo, identificamos que ciertos parámetros de rendimiento utilizados para las decisiones de escalado elástico pueden no ser fiables si no se tiene en cuenta la interferencia en el rendimiento. Al modelar la interferencia en el rendimiento, se muestra que estas métricas de rendimiento resultan fiables en un entorno multi-proveedor; y tercero, se identifica y muestra el impacto de la interferencia en la precisión del escalado elástico y se propone una solución para minimizar significativamente vulneraciones de rendimiento con un coste reducido.Postprint (published version

    The Design of a System Architecture for Mobile Multimedia Computers

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    This chapter discusses the system architecture of a portable computer, called Mobile Digital Companion, which provides support for handling multimedia applications energy efficiently. Because battery life is limited and battery weight is an important factor for the size and the weight of the Mobile Digital Companion, energy management plays a crucial role in the architecture. As the Companion must remain usable in a variety of environments, it has to be flexible and adaptable to various operating conditions. The Mobile Digital Companion has an unconventional architecture that saves energy by using system decomposition at different levels of the architecture and exploits locality of reference with dedicated, optimised modules. The approach is based on dedicated functionality and the extensive use of energy reduction techniques at all levels of system design. The system has an architecture with a general-purpose processor accompanied by a set of heterogeneous autonomous programmable modules, each providing an energy efficient implementation of dedicated tasks. A reconfigurable internal communication network switch exploits locality of reference and eliminates wasteful data copies

    A survey of techniques for reducing interference in real-time applications on multicore platforms

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    This survey reviews the scientific literature on techniques for reducing interference in real-time multicore systems, focusing on the approaches proposed between 2015 and 2020. It also presents proposals that use interference reduction techniques without considering the predictability issue. The survey highlights interference sources and categorizes proposals from the perspective of the shared resource. It covers techniques for reducing contentions in main memory, cache memory, a memory bus, and the integration of interference effects into schedulability analysis. Every section contains an overview of each proposal and an assessment of its advantages and disadvantages.This work was supported in part by the Comunidad de Madrid Government "Nuevas Técnicas de Desarrollo de Software de Tiempo Real Embarcado Para Plataformas. MPSoC de Próxima Generación" under Grant IND2019/TIC-17261

    Exploring traffic and QoS management mechanisms to support mobile cloud computing using service localisation in heterogeneous environments

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    In recent years, mobile devices have evolved to support an amalgam of multimedia applications and content. However, the small size of these devices poses a limit the amount of local computing resources. The emergence of Cloud technology has set the ground for an era of task offloading for mobile devices and we are now seeing the deployment of applications that make more extensive use of Cloud processing as a means of augmenting the capabilities of mobiles. Mobile Cloud Computing is the term used to describe the convergence of these technologies towards applications and mechanisms that offload tasks from mobile devices to the Cloud. In order for mobile devices to access Cloud resources and successfully offload tasks there, a solution for constant and reliable connectivity is required. The proliferation of wireless technology ensures that networks are available almost everywhere in an urban environment and mobile devices can stay connected to a network at all times. However, user mobility is often the cause of intermittent connectivity that affects the performance of applications and ultimately degrades the user experience. 5th Generation Networks are introducing mechanisms that enable constant and reliable connectivity through seamless handovers between networks and provide the foundation for a tighter coupling between Cloud resources and mobiles. This convergence of technologies creates new challenges in the areas of traffic management and QoS provisioning. The constant connectivity to and reliance of mobile devices on Cloud resources have the potential of creating large traffic flows between networks. Furthermore, depending on the type of application generating the traffic flow, very strict QoS may be required from the networks as suboptimal performance may severely degrade an application’s functionality. In this thesis, I propose a new service delivery framework, centred on the convergence of Mobile Cloud Computing and 5G networks for the purpose of optimising service delivery in a mobile environment. The framework is used as a guideline for identifying different aspects of service delivery in a mobile environment and for providing a path for future research in this field. The focus of the thesis is placed on the service delivery mechanisms that are responsible for optimising the QoS and managing network traffic. I present a solution for managing traffic through dynamic service localisation according to user mobility and device connectivity. I implement a prototype of the solution in a virtualised environment as a proof of concept and demonstrate the functionality and results gathered from experimentation. Finally, I present a new approach to modelling network performance by taking into account user mobility. The model considers the overall performance of a persistent connection as the mobile node switches between different networks. Results from the model can be used to determine which networks will negatively affect application performance and what impact they will have for the duration of the user's movement. The proposed model is evaluated using an analytical approac

    Mixed Criticality Systems - A Review : (13th Edition, February 2022)

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    This review covers research on the topic of mixed criticality systems that has been published since Vestal’s 2007 paper. It covers the period up to end of 2021. The review is organised into the following topics: introduction and motivation, models, single processor analysis (including job-based, hard and soft tasks, fixed priority and EDF scheduling, shared resources and static and synchronous scheduling), multiprocessor analysis, related topics, realistic models, formal treatments, systems issues, industrial practice and research beyond mixed-criticality. A list of PhDs awarded for research relating to mixed-criticality systems is also included

    캐시 분할 기술을 이용한 공유 라스트 레벨 캐시의 분할 정책에 따른 성능 민감도 연구

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    학위논문 (석사)-- 서울대학교 대학원 : 융합과학기술대학원 융합과학부, 2018. 2. 안정호.멀티 코어 시스템에서 여러 어플리케이션들을 동시에 실행할 때, 시스템 공유 자원(공유 캐시, 메인 메모리 등)에서 발생하는 경합/간섭은 일부 또는 모든 어플리케이션의 성능 저하를 유발할 수 있으며, 이를 양적으로 예측하는 것은 매우 어렵다. 특히, 여러 어플리케이션들이 한정된 공유 캐시 용량을 경합을 통해 나누어 사용하다 보면, 실시간 어플리케이션 또는 실행 시간이 중요한 어플리케이션이 다른 어플리케이션에 의해 캐시 점유율을 과도하게 빼앗겨 심각한 성능 저하를 겪을 수 있다. 이러한 공유 캐시에서 발생할 수 있는 부정적인 상황을 방지하기 위해서, 우선순위가 높은 어플리케이션에 적정 수준의 캐시 용량을 독립적으로 할당하는 방법을 사용할 수 있다. 이러한 방법은 실제 제품에 적용되기 전부터 광범위하게 연구되고 실험되어왔다. 인텔은 제온 프로세서 v3 제품 군부터 어플리케이션마다 공유 라스트 레벨 캐시를 분할/할당할 수 있는 Cache Allocation Technology(CAT) 기술을 적용하였다. 공유 캐시의 분할은 동일한 우선순위를 갖는 어플리케이션들의 집합 단위로 이루어진다. 캐시 분할 방법에서는 독립 분할과 중첩 분할 방식을 제공한다. 중첩 분할을 사용하면 우선순위가 높은 어플리케이션에 모든 캐시 영역을 할당할 수 있기 때문에 독립 분할을 사용할 때 보다 우선순위가 높은 어플리케이션의 성능을 최대화하는 데 유리할 수 있다. 그러나 이러한 직관적인 예상과는 반대 경향을 보일 가능성 또한 존재한다. 본 연구는 특정 어플리케이션의 성능을 최대화하기 위해 CAT를 사용할 때, 독립 분할과 중첩 분할의 성능을 하드웨어 실험을 통하여 비교하고 분석 프로그램과 시뮬레이션으로 그 원인을 파악하였다. 20 개 조합(어플리케이션 쌍) 중 14개 조합에서 독립 분할이 성능 우위(~12%)를 보였으며, 나머지 조합에서는 중첩 분할이 성능 우위(~16%)를 보였다. 독립 분할이 성능 우위를 보이는 경우는 중첩 분할 시 공유 영역에서 어플리케이션 간의 경쟁으로 인한 캐시 미스가 과도하게 발생하여 성능이 저하되는 것을 확인하였다. 시뮬레이션을 통해 이를 재현하였으며 캐시 미스가 증가한 것은 중첩 분할 시 캐시 교체 정책(예를 들어, least recently used 정책)을 제대로 적용할 수 없기 때문인 것을 확인하였다.제 1 장 서 론 1 제 1 절 연구동기 1 제 2 절 관련연구 및 배경 3 제 3 절 연구내용 7 제 2 장 독립 분할과 중첩 분할 성능 비교 9 제 1 절 독립 분할과 중첩 분할 설정 9 제 2 절 하드웨어 실험 환경 및 설정 10 제 3 절 어플레케이션 단독 수행 결과 12 제 4 절 독립 분할과 중철 분할 성능 결과 비교 분석 13 제 3 장 중첩 분할 성능 열화 원인 분석 20 제 1 절 캐시 교환 정책 및 중첩 분할 성능 연관성 20 제 2 절 시뮬레이션 실험 환경 및 설정 21 제 3 절 검증 실험 결과 22 제 4 장 결론 27 참고 문헌 28 Abstract 28Maste

    Branch Prediction For Network Processors

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    Originally designed to favour flexibility over packet processing performance, the future of the programmable network processor is challenged by the need to meet both increasing line rate as well as providing additional processing capabilities. To meet these requirements, trends within networking research has tended to focus on techniques such as offloading computation intensive tasks to dedicated hardware logic or through increased parallelism. While parallelism retains flexibility, challenges such as load-balancing limit its scope. On the other hand, hardware offloading allows complex algorithms to be implemented at high speed but sacrifice flexibility. To this end, the work in this thesis is focused on a more fundamental aspect of a network processor, the data-plane processing engine. Performing both system modelling and analysis of packet processing functions; the goal of this thesis is to identify and extract salient information regarding the performance of multi-processor workloads. Following on from a traditional software based analysis of programme workloads, we develop a method of modelling and analysing hardware accelerators when applied to network processors. Using this quantitative information, this thesis proposes an architecture which allows deeply pipelined micro-architectures to be implemented on the data-plane while reducing the branch penalty associated with these architectures
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