Using Fine-Grained Cycle Stealing to Improve Throughput, Efficiency and Response Time on a Dedicated Cluster while Maintaining Quality of Service

For various reasons, a dedicated cluster is not always fully utilized even when all of its processors are allocated to jobs. This occurs any time that a running job does not use 100% of each of the processors allocated to it. Keeping in mind the needs of both the cluster’s system administrators and its users, we would like to increase the throughput and efficiency of the cluster while maintaining or improving the average turnaround time of the jobs and the quality of service of the “primary” jobs originally scheduled on the cluster. To increase the throughput and efficiency of the cluster, we schedule background jobs to run concurrently with the primary jobs. However, to achieve our goal of maintaining or improving the average turnaround time of the jobs and the quality of service of the primary jobs, we investigate two methods of prioritizing the CPU usage of the primary and background jobs. The first method uses the existing “nice” mechanism in the 2.4 Linux kernel to give background processes a lower priority than primary processes. The second method involves modifying the 2.4 Linux kernel’s CPU scheduler to create a new guest process priority that prevents guest processes from running when primary processes are runnable. Our results come from empirical investigations using real production applications. Production runs using these applications are regularly performed in the dedicated cluster environment that we used for testing. Measurements of various statistics, such as wall time and CPU time, are taken directly from test runs that use these same production applications. This was helpful for comparison to results from models and synthetic applications. We found that using the existing nice mechanism significantly improves the throughput, efficiency and average turnaround time of the cluster but only at the expense of the quality of service of the primary jobs (primary job running times increased 5-25%). On the other hand, we can use the guest process priority to get similar improvements in throughput, efficiency and average turnaround time while not significantly impacting the quality of service of the primary jobs (primary job running times changed less than 1%)

Elastic computation placement in edge-based environments

Today, technologies such as machine learning, virtual reality, and the Internet of Things are integrated in end-user applications more frequently. These technologies demand high computational capabilities. Especially mobile devices have limited resources in terms of execution performance and battery life. The offloading paradigm provides a solution to this problem and transfers computationally intensive parts of applications to more powerful resources, such as servers or cloud infrastructure. Recently, a new computation paradigm arose which exploits the huge amount of end-user devices in the modern computing landscape - called edge computing. These devices encompass smartphones, tablets, microcontrollers, and PCs. In edge computing, devices cooperate with each other while avoiding cloud infrastructure. Due to the proximity among the participating devices, the communication latencies for offloading are reduced. However, edge computing brings new challenges in form of device fluctuation, unreliability, and heterogeneity, which negatively affect the resource elasticity. As a solution, this thesis proposes a computation placement framework that provides an abstraction for computation and resource elasticity in edge-based environments. The design is middleware-based, encompasses heterogeneous platforms, and supports easy integration of existing applications. It is composed of two parts: the Tasklet system and the edge support layer. The Tasklet system is a flexible framework for computation placement on heterogeneous resources. It introduces closed units of computation that can be tailored to generic applications. The edge support layer handles the characteristics of edge resources. It copes with fluctuation and unreliability by applying reactive and proactive task migration. Furthermore, the performance heterogeneity and the consequent bottlenecks are handled by two edge-specific task partitioning approaches. As a proof of concept, the thesis presents a fully-fledged prototype of the design, which is evaluated comprehensively in a real-world testbed. The evaluation shows that the design is able to substantially improve the resource elasticity in edge-based environments

Security in Distributed, Grid, Mobile, and Pervasive Computing

This book addresses the increasing demand to guarantee privacy, integrity, and availability of resources in networks and distributed systems. It first reviews security issues and challenges in content distribution networks, describes key agreement protocols based on the Diffie-Hellman key exchange and key management protocols for complex distributed systems like the Internet, and discusses securing design patterns for distributed systems. The next section focuses on security in mobile computing and wireless networks. After a section on grid computing security, the book presents an overview of security solutions for pervasive healthcare systems and surveys wireless sensor network security

Context-aware task scheduling in distributed computing systems

These days, the popularity of technologies such as machine learning, augmented reality, and big data analytics is growing dramatically. This leads to a higher demand of computational power not only for IT professionals but also for ordinary device users who benefit from new applications. At the same time, the computational performance of end-user devices increases to meet the demands of these resource-hungry applications. As a result, there is a coexistence of a huge demand of computational power on the one side and a large pool of computational resources on the other side. Bringing these two sides together is the idea of computational resource sharing systems which allow applications to forward computationally intensive workload to remote resources. This technique is often used in cloud computing where customers can rent computational power. However, we argue that not only cloud resources can be used as offloading targets. Rather, idle CPU cycles from end-user administered devices at the edge of the network can be spontaneously leveraged as well. Edge devices, however, are not only heterogeneous in their hardware and software capabilities, they also do not provide any guarantees in terms of reliability or performance. Does it mean that either the applications that require further guarantees or the unpredictable resources need to be excluded from such a sharing system? In this thesis, we propose a solution to this problem by introducing the Tasklet system, our approach for a computational resource sharing system. The Tasklet system supports computation offloading to arbitrary types of devices, including stable cloud instances as well as unpredictable end-user owned edge resources. Therefore, the Tasklet system is structured into multiple layers. The lowest layer is a best-effort resource sharing system which provides lightweight task scheduling and execution. Here, best-effort means that in case of a failure, the task execution is dropped and that tasks are allocated to resources randomly. To provide execution guarantees such as a reliable or timely execution, we add a Quality of Computation (QoC) layer on top of the best-effort execution layer. The QoC layer enforces the guarantees for applications by using a context-aware task scheduler which monitors the available resources in the computing environment and performs the matchmaking between resources and tasks based on the current state of the system. As edge resources are controlled by individuals, we consider the fact that these users need to be able to decide with whom they want to share their resources and for which price. Thus, we add a social layer on top of the system that allows users to establish friendship connections which can then be leveraged for social-aware task allocation and accounting of shared computation

‘Digital surveillance’ from the perspective of ‘Christian Freedom’ : a theological assessment in conversation with Martin Luther and Dietrich Bonhoeffer

Thesis (PhD)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Digital surveillance as a dominant phenomenon of current life is increasingly coming under scrutiny by sociological and economic research because of its impact on individuals and societies. Theologians can contribute to this discourse through their focus on the human-divine relationship and its ethical implications. This thesis investigates in what way Christian freedom according to the Lutheran tradition can speak critically and constructively to the problematic aspects of digital monitoring. To this end the practice of pervasive data harvesting and processing by state and commercial operators is placed within a wider framework of historical, cultural, political, social, economic and technological parameters. This analysis raises serious concerns about governance, the handling of power and the role of technology, but also about human dignity, the notion of human freedom and the overall understanding of the human person as such. The dilemma of an adequate response to these challenges has to do with human ambiguity, resignation and dependency on the digital medium. The subsequent exploration of Christian freedom first relies on Luther’s seminal considerations on freedom, which reflect his God-related anthropology. As a divine gift of grace, granting justification, forgiveness and a liberated existence in Christ, freedom is realized as loving commitment to others in faithfulness towards God. In society, freedom unfolds its dynamic within the twofold rule of God in the worldly and the spiritual kingdom. Bonhoeffer portrays freedom as anchored in the reconciliation reality revealed in Christ, characterizing it as ‘creaturely freedom’ for God, from creation and for others. It is the basis for a new humanity in conformation to Christ and a life that is determined by accountability before God and mutual human responsibility. The ethical claim embodied in ‘the other’ is honoured in love and obedience towards the divine will and in vicarious representative action for others. To describe the specific tasks of Christians and government in society, Bonhoeffer leans on Luther’s twokingdoms- approach, appropriating it for his own time. A Reformation-based theology thus identifies the worldview of the digital surveillance paradigm as strongly self-referential and devoid of a transcendent perspective. This results in an inappropriate view of the human person and a self-centred concept of freedom, which abets the neglect of others, the avoiding of responsibility and the danger of dispensing with moral considerations. Christian freedom constitutes an antidote, emphasizing the gift-character of human life, the liberation from perpetual self-justification and the inescapable judgement of data permanence through God’s judgement of grace. In rejecting the utilitarian calculus of digital abstraction, it affirms the wholeness and value of individual personhood. Against ideas of freedom as convenience, predictability and risk-free safety and its side-effects of dependency and (self)objectification, freedom is upheld as reciprocity, grounded in bonds of trust, wherein responsibility is embraced as divine empowerment to serve others and for genuine ‘self-realization’. This approach can represent an alternative way of living and acting in a digitally dominated world. The critical assessment of digital surveillance shows the urgent need to find agreement on certain values based on a shared experience of humanity.AFRIKAANSE OPSOMMING: Digitale bewaking, as ’n dominante fenomeen van die hedendaagse lewe, is toenemend die onderwerp van sosiologiese en ekonomiese navorsing vanweë die impak op individue en samelewings. Teoloë kan tot hierdie diskoers bydra deur hulle fokus op die verhouding tussen mens en God en die etiese implikasies daarvan. Hierdie tesis ondersoek in watter opsig Christelike vryheid volgens die Lutherse tradisie krities en konstruktief uitspraak lewer oor die problematiese aspekte van digitale monitering. Vir hierdie doel word die praktyk van omvattende data-insameling en -verwerking deur staats- en kommersiële operateurs binne ’n breë historiese, kulturele, politieke, sosiale, ekonomiese en tegnologiese raamwerk gestel. Hierdie analise wek ernstige kommer oor bestuursgedrag, die hantering van mag en die rol van tegnologie, maar ook oor menswaardigheid, die konsep van menslike vryheid en die verstaan van die mens in die algemeen. Die dilemma van ’n gepaste antwoord op hierdie uitdagings het te make met menslike ambivalensie, oorgawe aan en afhanklikheid van die digitale medium. Die daaropvolgende ondersoek van Christelike vryheid maak eerstens staat op Luther se seminale oorwegings wat sy God-verwante antropologie reflekteer. Vryheid word beskou as ’n goddelike gawe van genade, die skenk van regverdiging, vergifnis en ’n bevryde bestaan in Christus. Dit word verwerklik in ’n liefdevolle verbondenheid met ander mense wat uit getroudheid aan God spruit. In die samelewing ontsluit vryheid sy dinamiek binne die tweevoudige heerskappy van God in die wêreldse en die geestelike koninkryk. Bonhoeffer beeld vryheid uit as geanker in die werklikheid van versoening soos in Christus geopenbaar. Hy karakteriseer dit as ‘vryheid van die kreatuur’ vir God, vanuit die skepping en ter wille van ander. Dit is die basis vir ’n nuwe menslikheid in ooreenstemming met Christus en ’n lewe wat bepaal word deur aanspreeklikheid teenoor God en wedersydse menslike verantwoordelikheid. Die etiese aanspraak beliggaam in ‘die ander’ word eerbiedig in liefde en gehoorsamheid teenoor die goddelike wil en in die plaasvervangende verteenwoordiging vir ander. In sy beskrywing van die spesifieke take van Christene en regerings in die samelewing, steun Bonhoeffer op Luther se twee-koninkryke-benadering en pas dit aan vir sy eie tyd ’n Reformasie-gebaseerde teologie identifiseer dus die wêreldbeeld van die digitale bewakingsparadigma as sterk self-verwysend en sonder ’n transendente perspektief. Dit lei tot ’n misplaaste opvatting van die mens en ’n self-behepte voorstelling van vryheid wat die verontagsaming van ander, vermyding van verantwoordelikheid en die gevaar van die minagting van morele oorwegings bevorder. Christelike vryheid stel ’n teenmiddel daar wat die geskenk-karakter van die menslike lewe beklemtoon asook die bevryding van permanente selfregverdiging en van die onontkombare oordeel van datapermanensie deur God se oordeel van genade bewerkstellig. Deur nuttigheidslogika van digitale abstraksie te verwerp, bevestig Christelike vryheid die integriteit en waarde van individuele persoonskap. Teenoor die idees van vryheid as gerieflikheid, voorspelbaarheid en risikolose veiligheid, met sy newe-effekte van afhanklikheid en (self)objektivering, word vryheid as wederkerig verstaan, gegrond in ’n vertrouensverbond, waarbinne verantwoordelikheid aangegryp word as goddelike bemagtiging om ander te dien en ware self-verwesentliking te bereik. Hierdie benadering verteenwoordig ’n alternatiewe manier om binne ’n digitale wêreld te leef en te handel. Die kritiese ontleding van digitale bewaking toon die dringende behoefte om ooreenstemming te vind oor sekere waardes wat op ’n gedeelte ondervinding van menswees gebaseer is.Doctora