A Byzantine Fault Tolerant Distributed Commit Protocol

In this paper, we present a Byzantine fault tolerant distributed commit protocol for transactions running over untrusted networks. The traditional two-phase commit protocol is enhanced by replicating the coordinator and by running a Byzantine agreement algorithm among the coordinator replicas. Our protocol can tolerate Byzantine faults at the coordinator replicas and a subset of malicious faults at the participants. A decision certificate, which includes a set of registration records and a set of votes from participants, is used to facilitate the coordinator replicas to reach a Byzantine agreement on the outcome of each transaction. The certificate also limits the ways a faulty replica can use towards non-atomic termination of transactions, or semantically incorrect transaction outcomes.Comment: To appear in the proceedings of the 3rd IEEE International Symposium on Dependable, Autonomic and Secure Computing, 200

A Comparative Analysis of STM Approaches to Reduction Operations in Irregular Applications

As a recently consolidated paradigm for optimistic concurrency in modern multicore architectures, Transactional Memory (TM) can help to the exploitation of parallelism in irregular applications when data dependence information is not available up to run- time. This paper presents and discusses how to leverage TM to exploit parallelism in an important class of irregular applications, the class that exhibits irregular reduction patterns. In order to test and compare our techniques with other solutions, they were implemented in a software TM system called ReduxSTM, that acts as a proof of concept. Basically, ReduxSTM combines two major ideas: a sequential-equivalent ordering of transaction commits that assures the correct result, and an extension of the underlying TM privatization mechanism to reduce unnecessary overhead due to reduction memory updates as well as unnecesary aborts and rollbacks. A comparative study of STM solutions, including ReduxSTM, and other more classical approaches to the parallelization of reduction operations is presented in terms of time, memory and overhead.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

HERO: Heterogeneous Embedded Research Platform for Exploring RISC-V Manycore Accelerators on FPGA

Heterogeneous embedded systems on chip (HESoCs) co-integrate a standard host processor with programmable manycore accelerators (PMCAs) to combine general-purpose computing with domain-specific, efficient processing capabilities. While leading companies successfully advance their HESoC products, research lags behind due to the challenges of building a prototyping platform that unites an industry-standard host processor with an open research PMCA architecture. In this work we introduce HERO, an FPGA-based research platform that combines a PMCA composed of clusters of RISC-V cores, implemented as soft cores on an FPGA fabric, with a hard ARM Cortex-A multicore host processor. The PMCA architecture mapped on the FPGA is silicon-proven, scalable, configurable, and fully modifiable. HERO includes a complete software stack that consists of a heterogeneous cross-compilation toolchain with support for OpenMP accelerator programming, a Linux driver, and runtime libraries for both host and PMCA. HERO is designed to facilitate rapid exploration on all software and hardware layers: run-time behavior can be accurately analyzed by tracing events, and modifications can be validated through fully automated hard ware and software builds and executed tests. We demonstrate the usefulness of HERO by means of case studies from our research

Bridging the Organizational Divide -- The Making of a Nonprofit Merger

Nonprofit, community-based housing development organizations have only recently become significant players in the provision of affordable housing, at least in the United States. Historically, this job was left either in the hands of builders, developers, lenders and landlords of the business sector or in the care of agencies, planners and policymakers of the public sector. Only in the past 30 years has the provision of affordable housing moved beyond the familiar domains of the market and the state. A host of nonprofit organizations is now playing a larger role in constructing new housing, rehabilitating older housing, managing rentals and bringing home ownership within the reach of thousands of people for whom the American dream has proved elusive.The growth of these third-sector organizations has been both rapid and impressive, but it also has been uneven. Across the country, there are places where nonprofit housing development organizations are both plentiful and productive, supported by sophisticated networks of interorganizational collaboration, public funding, private financing and technical assistance. There are many other communities, however, where no nonprofits are engaged in affordable housing or where the ones that do exist are very new or very small, accounting for only a handful of new housing units every year.Lying between these two extremes are those communities where multiple nonprofits of varying size serve a similar geographic area, each producing a modest but respectable number of housing units; each competing for constituents, funding and development opportunities; each struggling to survive. The organizations that find themselves in this uncomfortable situation often confront a special set of challenges. They are productive, but not prolific. They are effective, but not efficient. They are successful, but not sustainable. Indeed, they are frequently quite precarious. The loss of a single staff person, the delay of a single project or the adverse decision of a single funder can threaten not only their short-term chances for success, but their long term prospects for survival.Those who sponsor and fund such organizations sometimes find themselves in a situation where competition among multiple nonprofits is weakening them all. In these cases, the sponsoring and funding organizations have taken different tacks to address this problem. In some cases, they have acted to strengthen every nonprofit, while working to increase the division of labor or the division of territory among them. In other cases, they have acted to strengthen one (or more) nonprofit at the expense of the others, culling weaker performers from the herd.While these have been the most common approaches for dealing with the weaknesses that organizational competition and duplication can sometimes create, a third alternative has been gaining ground. Multiple nonprofits, operating within the same jurisdiction, are being encouraged to collaborate -- even to the point of merging their programs, assets and hard-won identities.Why is collaboration gaining in popularity? A financial explanation would be that it is becoming harder to find enough resources to strengthen every nonprofit to the same degree, funding multiple nonprofits to serve a similar clientele in the same locale. There is also the political reality that public and private funders find it difficult to choose easily (or accurately) which nonprofits should live -- and which should die. There is a practical explanation as well. Collaboration is becoming a strategy of choice simply because it is proving to be an unusually effective way of achieving greater productivity, efficiency and sustainability. When a collaborative (or a merger) is carefully crafted, the nonprofit partners do a better job together than they did apart. This is not true in every case, of course.Read the full report for lessons in organizational matchmaking and the making of a nonprofit merger

Managing the trade-off implications of global supply

The cost versus response trade-off is a growing logistics issue due to many markets being increasingly characterized by demand uncertainty and shorter product life cycles. This is exacerbated further with supply increasingly moving to low cost global sources. However, the poor response implications of global supply are often not addressed or even acknowledged when undertaking such decisions. Consequently, various practical approaches to minimising, postponing or otherwise managing the impact of the demand uncertainty are often only adopted retrospectively. Even though such generic solutions are documented through case examples we lack effective tools and concepts to support the proactive identification and resolution of such trade-offs. This paper reports on case-based theory building research, involving three cases from the UK and USA used in developing a conceptual model with associated tools, in support of such a process

Boosting Multi-Core Reachability Performance with Shared Hash Tables

This paper focuses on data structures for multi-core reachability, which is a key component in model checking algorithms and other verification methods. A cornerstone of an efficient solution is the storage of visited states. In related work, static partitioning of the state space was combined with thread-local storage and resulted in reasonable speedups, but left open whether improvements are possible. In this paper, we present a scaling solution for shared state storage which is based on a lockless hash table implementation. The solution is specifically designed for the cache architecture of modern CPUs. Because model checking algorithms impose loose requirements on the hash table operations, their design can be streamlined substantially compared to related work on lockless hash tables. Still, an implementation of the hash table presented here has dozens of sensitive performance parameters (bucket size, cache line size, data layout, probing sequence, etc.). We analyzed their impact and compared the resulting speedups with related tools. Our implementation outperforms two state-of-the-art multi-core model checkers (SPIN and DiVinE) by a substantial margin, while placing fewer constraints on the load balancing and search algorithms.Comment: preliminary repor