Partial aggregation for collective communication in distributed memory machines

High Performance Computing (HPC) systems interconnect a large number of Processing Elements (PEs) in high-bandwidth networks to simulate complex scientific problems. The increasing scale of HPC systems poses great challenges on algorithm designers. As the average distance between PEs increases, data movement across hierarchical memory subsystems introduces high latency. Minimizing latency is particularly challenging in collective communications, where many PEs may interact in complex communication patterns. Although collective communications can be optimized for network-level parallelism, occasional synchronization delays due to dependencies in the communication pattern degrade application performance. To reduce the performance impact of communication and synchronization costs, parallel algorithms are designed with sophisticated latency hiding techniques. The principle is to interleave computation with asynchronous communication, which increases the overall occupancy of compute cores. However, collective communication primitives abstract parallelism which limits the integration of latency hiding techniques. Approaches to work around these limitations either modify the algorithmic structure of application codes, or replace collective primitives with verbose low-level communication calls. While these approaches give fine-grained control for latency hiding, implementing collective communication algorithms is challenging and requires expertise knowledge about HPC network topologies. A collective communication pattern is commonly described as a Directed Acyclic Graph (DAG) where a set of PEs, represented as vertices, resolve data dependencies through communication along the edges. Our approach improves latency hiding in collective communication through partial aggregation. Based on mathematical rules of binary operations and homomorphism, we expose data parallelism in a respective DAG to overlap computation with communication. The proposed concepts are implemented and evaluated with a subset of collective primitives in the Message Passing Interface (MPI), an established communication standard in scientific computing. An experimental analysis with communication-bound microbenchmarks shows considerable performance benefits for the evaluated collective primitives. A detailed case study with a large-scale distributed sort algorithm demonstrates, how partial aggregation significantly improves performance in data-intensive scenarios. Besides better latency hiding capabilities with collective communication primitives, our approach enables further optimizations of their implementations within MPI libraries. The vast amount of asynchronous programming models, which are actively studied in the HPC community, benefit from partial aggregation in collective communication patterns. Future work can utilize partial aggregation to improve the interaction of MPI collectives with acclerator architectures, and to design more efficient communication algorithms

Software for Exascale Computing - SPPEXA 2016-2019

This open access book summarizes the research done and results obtained in the second funding phase of the Priority Program 1648 "Software for Exascale Computing" (SPPEXA) of the German Research Foundation (DFG) presented at the SPPEXA Symposium in Dresden during October 21-23, 2019. In that respect, it both represents a continuation of Vol. 113 in Springer’s series Lecture Notes in Computational Science and Engineering, the corresponding report of SPPEXA’s first funding phase, and provides an overview of SPPEXA’s contributions towards exascale computing in today's sumpercomputer technology. The individual chapters address one or more of the research directions (1) computational algorithms, (2) system software, (3) application software, (4) data management and exploration, (5) programming, and (6) software tools. The book has an interdisciplinary appeal: scholars from computational sub-fields in computer science, mathematics, physics, or engineering will find it of particular interest

Tangled root: The paradoxical development of British Columbia's tree planting industry.

British Columbian tree planters have cultivated a reputation for being countercultural mavericks within the world of forestry. While this standing is well earned in many respects, it also implies that the job is ethically structured in a way that somehow opposes industrial resource extraction like clear-cut logging. Contrary to these perceptions, this study will show how throughout the history of tree planting in B.C. reforestation workers have been given incentive to fulfill the forest industry's mandate to plant trees faster and better, thereby acting as critical participants in maintaining the legitimacy of the modern forest industry. I will show that despite their reputations or personal values, tree planters in British Columbia have also existed - both philosophically and practically - in a symbiotic relationship with intensive harvesting practices. Far from solely being an idealistic social experiment, this prototypical model of a sustainable industry became successful through the displacement of the distinction between binaries like green and corporate, counterculture and capitalist, as well as tree-huggers and loggers. As a result, it is common for contemporary reforestation workers to exude an occupational culture that is bohemian but also maintains a widespread emphasis upon ultra-efficiency, competition, and money-making - traits that have generally intensified over time. --P. ii.The original print copy of this thesis may be available here: http://wizard.unbc.ca/record=b175477

Mobile bodies : train travel and practices of movement

This thesis investigates experiences of railway travel from a passenger perspective by looking at how passengers move through and dwell within spaces of the railway journey. It responds to a lack of attention to diverse processual enactments and theorisations of processes and practices that constitute these flows. Challenging both the theory that this particular 'space of flows' constitutes a non-place that is characterised by placelessness, and theories that rely on aggregate models of movement that serve to pacify the body, this thesis speaks to the neglected transient experience that acknowledges how the railway journey is continually brought into being by passengers through practice rather than given a-priori. It is based on in-depth empirical research that focuses on long-distance, intercity journeys as a particular space of flows. It develops a descriptive, multi-method approach to investigate what a travelling body is and how a body becomes a travelling body; how and to what extent travel-time is planned, organised, used and valued; and how the experience of time and space transform over the duration of a journey. For many, and contrary to economically-productivist studies, the railway journey is not a wasted time, but is valued and put to use in a variety of different ways that fold through and are integrally-linked to the commitments, motivations and obligations of other time-spaces. The resulting heterogeneity of practices within the confined space of the railway carriage also has significant implications for the sociality and forms of responsibility that develop. However, certain parts of the journey are more valuable than others and within this space of flows are many durations of immobility and passivity. Nevertheless, and contrary to other practice-based studies that privilege the body-in-action, passivity does not necessarily constitute a weak form of inhabiting the world. This research demonstrates how multiple configurations of passivity come into play at different points during the railway journey to assist in making the process of travel easier. In sum, this thesis mobilises new ways of looking at transient spaces which attempt to move beyond a sedentary metaphysics of space

Anthropology of Color

The field of color categorization has always been intrinsically multi- and inter-disciplinary, since its beginnings in the nineteenth century. The main contribution of this book is to foster a new level of integration among different approaches to the anthropological study of color. The editors have put great effort into bringing together research from anthropology, linguistics, psychology, semiotics, and a variety of other fields, by promoting the exploration of the different but interacting and complementary ways in which these various perspectives model the domain of color experience. By so doing, they significantly promote the emergence of a coherent field of the anthropology of color