76 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Online Algorithms with Randomly Infused Advice

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    We introduce a novel method for the rigorous quantitative evaluation of online algorithms that relaxes the "radical worst-case" perspective of classic competitive analysis. In contrast to prior work, our method, referred to as randomly infused advice (RIA), does not make any assumptions about the input sequence and does not rely on the development of designated online algorithms. Rather, it can be applied to existing online randomized algorithms, introducing a means to evaluate their performance in scenarios that lie outside the radical worst-case regime. More concretely, an online algorithm ALG with RIA benefits from pieces of advice generated by an omniscient but not entirely reliable oracle. The crux of the new method is that the advice is provided to ALG by writing it into the buffer ? from which ALG normally reads its random bits, hence allowing us to augment it through a very simple and non-intrusive interface. The (un)reliability of the oracle is captured via a parameter 0 ? ? ? 1 that determines the probability (per round) that the advice is successfully infused by the oracle; if the advice is not infused, which occurs with probability 1 - ?, then the buffer ? contains fresh random bits (as in the classic online setting). The applicability of the new RIA method is demonstrated by applying it to three extensively studied online problems: paging, uniform metrical task systems, and online set cover. For these problems, we establish new upper bounds on the competitive ratio of classic online algorithms that improve as the infusion parameter ? increases. These are complemented with (often tight) lower bounds on the competitive ratio of online algorithms with RIA for the three problems

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Performance, memory efficiency and programmability: the ambitious triptych of combining vertex-centricity with HPC

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    The field of graph processing has grown significantly due to the flexibility and wide applicability of the graph data structure. In the meantime, so has interest from the community in developing new approaches to graph processing applications. In 2010, Google introduced the vertex-centric programming model through their framework Pregel. This consists of expressing computation from the perspective of a vertex, whilst inter-vertex communications are achieved via data exchanges along incoming and outgoing edges, using the message-passing abstraction provided. Pregel ’s high-level programming interface, designed around a set of simple functions, provides ease of programmability to the user. The aim is to enable the development of graph processing applications without requiring expertise in optimisation or parallel programming. Such challenges are instead abstracted from the user and offloaded to the underlying framework. However, fine-grained synchronisation, unpredictable memory access patterns and multiple sources of load imbalance make it difficult to implement the vertex centric model efficiently on high performance computing platforms without sacrificing programmability. This research focuses on combining vertex-centric and High-Performance Comput- ing (HPC), resulting in the development of a shared-memory framework, iPregel, which demonstrates that a performance and memory efficiency similar to that of non-vertex- centric approaches can be achieved while preserving the programmability benefits of vertex-centric. Non-volatile memory is then explored to extend single-node capabilities, during which multiple versions of iPregel are implemented to experiment with the various data movement strategies. Then, distributed memory parallelism is investigated to overcome the resource limitations of single node processing. A second framework named DiP, which ports applicable iPregel ’s optimisations to distributed memory, prioritises performance to high scalability. This research has resulted in a set of techniques and optimisations illustrated through a shared-memory framework iPregel and a distributed-memory framework DiP. The former closes a gap of several orders of magnitude in both performance and memory efficiency, even able to process a graph of 750 billion edges using non-volatile memory. The latter has proved that this competitiveness can also be scaled beyond a single node, enabling the processing of the largest graph generated in this research, comprising 1.6 trillion edges. Most importantly, both frameworks achieved these performance and capability gains whilst also preserving programmability, which is the cornerstone of the vertex-centric programming model. This research therefore demonstrates that by combining vertex-centricity and High-Performance Computing (HPC), it is possible to maintain performance, memory efficiency and programmability

    LIPIcs, Volume 274, ESA 2023, Complete Volume

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    LIPIcs, Volume 274, ESA 2023, Complete Volum

    Page size aware cache prefetching

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    The increase in working set sizes of contemporary applications outpaces the growth in cache sizes, resulting in frequent main memory accesses that deteriorate system per- formance due to the disparity between processor and memory speeds. Prefetching data blocks into the cache hierarchy ahead of demand accesses has proven successful at attenuating this bottleneck. However, spatial cache prefetchers operating in the physical address space leave significant performance on the table by limiting their pattern detection within 4KB physical page boundaries when modern systems use page sizes larger than 4KB to mitigate the address translation overheads. This paper exploits the high usage of large pages in modern systems to increase the effectiveness of spatial cache prefetch- ing. We design and propose the Page-size Propagation Module (PPM), a µarchitectural scheme that propagates the page size information to the lower-level cache prefetchers, enabling safe prefetching beyond 4KB physical page boundaries when the accessed blocks reside in large pages, at the cost of augmenting the first-level caches’ Miss Status Holding Register (MSHR) entries with one additional bit. PPM is compatible with any cache prefetcher without implying design modifications. We capitalize on PPM’s benefits by designing a module that consists of two page size aware prefetchers that inherently use different page sizes to drive prefetching. The composite module uses adaptive logic to dynamically enable the most appropriate page size aware prefetcher. Finally, we show that the proposed designs are transparent to which cache prefetcher is used. We apply the proposed page size exploitation techniques to four state-of-the-art spatial cache prefetchers. Our evalua- tion shows that our proposals improve single-core geomean performance by up to 8.1% (2.1% at minimum) over the original implementation of the considered prefetchers, across 80 memory-intensive workloads. In multi-core contexts, we report geomean speedups up to 7.7% across different cache prefetchers and core configurations.This work is supported by the Spanish Ministry of Science and Technology through the PID2019-107255GB project, the Generalitat de Catalunya (contract 2017-SGR-1414), the European Union Horizon 2020 research and innovation program under grant agreement No 955606 (DEEP-SEA EU project), the National Science Foundation through grants CNS-1938064 and CCF-1912617, and the Semiconductor Research Corporation project GRC 2936.001. Georgios Vavouliotis has been supported by the Spanish Ministry of Economy, Industry, and Competitiveness and the European Social Fund under the FPI fellowship No. PRE2018-087046. Marc Casas has been partially supported by the Grant RYC2017-23269 funded by MCIN/AEI/10.13039/501100011033 and ESF ‘Investing in your future’.Peer ReviewedPostprint (author's final draft

    Studium sídelních systémů pomocí lokalizačních dat mobilních telefonů

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    Settlement systems, the large-scale manifestation of the spatial organization of human society, are the frequent object of human geography studies. Mobile positioning data have been used in recent decades as a unique source on human activities in space, but robust methodologies to generate datasets from them that would be comparable in accuracy to conventional sources such as census data or travel diaries have still been lacking. This thesis aims to bridge the gap by describing in detail how to generate population distribution and commuting datasets from mobile positioning sources with the mentioned accuracy using ma- chine learning and ancillary geospatial data, including proper treatment of data privacy and artifacts inherent to mobile positioning, and to illustrate their ca- pabilities by building hierarchical settlement system models from them. Several further possible refinements are presented and discussed. 1Sídelní systémy jsou jakožto významná složka makrogeografické organizace lidské společnosti častým objektem studia sociální geografie. Lokalizační data mobilních telefonů jsou v posledních dekádách oblíbená jako unikátní zdroj o lidských aktivitách v prostoru, stále však chybí spolehlivé metody, jak z nich vytvořit datové sady s přesností porovnatelnou s konvenčními zdroji, jako jsou data ze sčítání lidu nebo cestovní deníky. Tato práce si klade za cíl zaplnit tuto mezeru detailním popisem tvorby datových sad o počtech obyvatel a dojížďce z lokalizačních dat mobilních telefonů se zmíněnou úrovní přesnosti za pomoci strojového učení a pomocných geografických dat, včetně správného ošetření anonymity dat i artefaktů plynoucích z principů fungování mobilní sítě, a ilustrovat možnosti těchto výsledků tvorbou hierarchického modelu sídelního systému. Jsou představeny a diskutovány další možnosti rozvoje. 1Department of Applied Geoinformatics and CartographyKatedra aplikované geoinformatiky a kartografiePřírodovědecká fakultaFaculty of Scienc

    Management of Technological Innovation in Developing and Developed Countries

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    It is widely accepted that technology is one of the forces driving economic growth. Although more and more new technologies have emerged, various evidence shows that their performances were not as high as expected. In both academia and practice, there are still many questions about what technologies to adopt and how to manage these technologies. The 15 articles in this book aim to look into these questions. There are quite many features in this book. Firstly, the articles are from both developed countries and developing countries in Asia, Africa and South and Middle America. Secondly, the articles cover a wide range of industries including telecommunication, sanitation, healthcare, entertainment, education, manufacturing, and financial. Thirdly, the analytical approaches are multi-disciplinary, ranging from mathematical, economic, analytical, empirical and strategic. Finally, the articles study both public and private organizations, including the service industry, manufacturing industry, and governmental organizations. Given its wide coverage and multi-disciplines, the book may be useful for both academic research and practical management

    Instilling reflective practice – The use of an online portfolio in innovative optometric education Accepted as: e‐poster Paper no. 098

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    At UCLAN we are breaking the mould and have developed a blended learning MSci optometry programme which is the first blended learning course in optometric education in the UK and the first to use a practice-based online portfolio. Optometry has traditionally been taught as a 3‐year undergraduate programme. Upon successful graduation, students are required to complete a year in practice and meet the General Optical Council's (GOC) “ability to” core competencies. However, a recent study by the GOC found that 76% of students felt unprepared for professional practice with insufficient clinical experience and in response, the GOC is currently undertaking an educational strategic review. To ensure the students receive high-quality clinical experience in the workplace, we have developed an online logbook and portfolio. Students log their experiences, learning points and reflections. The portfolio is closely monitored both by the student's mentor in practice and by academic staff. The content and reflections logged by the students then helps to drive the face to face teaching, small group discussions and clinical experiences provided by the university

    The politics of internet infrastructure: communication policy, governmentality and subjectivation in Chhattisgarh, India

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    This thesis examines the role of internet infrastructure and its associated discourses in processes of governmentality and subject formation in low and middle-income countries of the global South. Using data collected in the central Indian state of Chhattisgarh as its core case, it asks questions about the interrelationship between policy and political discourse, new information and communications infrastructure, private capital, and how citizens come to know and/or experience internet infrastructure in their everyday lives. Since 2014, The National Optical Fibre Network (NOFN, which began in 2011 under the then UPA government) has been reshaped and rebranded as part of ‘Digital India’ by Prime Minister Narendra Modi and his far-right Hindutva Bharatiya Janata Party (BJP). Alongside the cables and connectivity, the BJP and allied Hindu extremist organisations have targeted minorities and women through mob violence and (on and offline) hate speech, while a small number of crony capitalist corporations have seen immense profits. Unpicking the links between these processes, the thesis argues that internet infrastructure has become crucial to expanding a particular unregulated brand of capitalism and to narrowing civic subjectivities. Infrastructures constellate and circulate material and symbolic goods in an institutionalised manner to produce collectivities. Using discourse analysis shows that since the late 1980s, in a context of increasing neoliberalism, internet infrastructure emerged within a discursive regime marked by the fetishisation of systems rationality, enumeration, scientism and economism to produce what can be called digital governmentality. Digital governmentality enables and reinforces a centralised Hindu nationalism mediated by digital technologies and networks. Using semi-structured interviews and participant observation in the city of Ambikapur, and close to 50 villages in Surguja district of Chhattisgarh, data chapters describe a wide range of ‘infrastructural practices.’ The analysis centres on how subjects imagine, frame and experience these practices. Dominant caste groups in Ambikapur seek to subvert governmentality in practice but also uphold and reproduce the rationalities that drive governmental authority – such as efficiency and transparency. Adivasis (indigenous groups) who reside in surrounding rural areas are subject to a political economic regime overdetermined by coal mining and destruction of their land, forests and water resources. Internet infrastructure is non-existent or broken, along with other missing infrastructural substrates such as electricity and water. Adivasis face infrastructural control as a specific mode of governmentality where power is exerted not from the top in directly coercive ways but rather through mundane infrastructural practices, thereby exerting authority in procedural ways. In other instances, Adivasis’ processes of subject formation are entangled with (the reality and promise of) internet infrastructure in complex ways – ranging from cruel optimism to social haunting. The thesis makes an original contribution to the emerging sub-field of infrastructure studies by providing a new way of studying communicative infrastructures involving: a renewed emphasis on relationality (infrastructures, governmentality and subjectivation as relational processes and practices); situating internet infrastructures within broader infrastructures; and a historical analysis of how infrastructure is caught up in exercise of power relations. With significant emphasis on the concerns and interests of indigenous peoples in India, the final chapters of the thesis also contribute to a decolonisation of media and communications as a field, and to avoiding orientalist essentialism
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