Termination detection for fine-grained message-passing architectures

Barrier primitives provided by standard parallel programming APIs are the primary means by which applications implement global synchronisation. Typically these primitives are fully-committed to synchronisation in the sense that, once a barrier is entered, synchronisation is the only way out. For message-passing applications, this raises the question of what happens when a message arrives at a thread that already resides in a barrier. Without a satisfactory answer, barriers do not interact with message-passing in any useful way. In this paper, we propose a new refutable barrier primitive that combines with message-passing to form a simple, expressive, efficient, well-defined API. It has a clear semantics based on termination detection, and supports the development of both globally-synchronous and asynchronous parallel applications. To evaluate the new primitive, we implement it in a prototype large-scale message-passing machine with 49,152 RISC-V threads distributed over 48 FPGAs. We show that hardware support for the primitive leads to a highly-efficient implementation, capable of synchronisation rates that are an order-of-magnitude higher than what is achievable in software. Using the primitive, we implement synchronous and asynchronous versions of a range of applications, observing that each version can have significant advantages over the other, depending on the application. Therefore, a barrier primitive supporting both styles can greatly assist the development of parallel programs.Funded by EPSRC grant EP/N031768/1 (POETS project

General hardware multicasting for fine-grained message-passing architectures

Manycore architectures are increasingly favouring message-passing or partitioned global address spaces (PGAS) over cache coherency for reasons of power efficiency and scalability. However, in the absence of cache coherency, there can be a lack of hardware support for one-to-many communication patterns, which are prevalent in some application domains. To address this, we present new hardware primitives for multicast communication in rack-scale manycore systems. These primitives guarantee delivery to both colocated and distributed destinations, and can capture large unstructured communication patterns precisely. As a result, reliable multicast transfers among any number of software tasks, connected in any topology, can be fully offloaded to hardware. We implement the new primitives in a research platform consisting of 50K RISC-V threads distributed over 48 FPGAs, and demonstrate significant performance benefits on a range of applications expressed using a high-level vertex-centric programming model

Applying provenance in APT monitoring and analysis: Practical challenges for scalable, efficient and trustworthy distributed provenance

Advanced Persistent Threats (APT) are a class of security threats in which a well-resourced attacker targets a specific individual or organisation with a predefined goal. This typically involves exfiltration of confidential material, although increasingly attacks target the encryption or destruction of mission critical data. With traditional prevention and detection mechanisms failing to stem the tide of such attacks, there is a pressing need for new monitoring and analysis tools that reduce both false-positive rates and the cognitive burden on human analysts. We propose that local and distributed provenance metadata can simplify and improve monitoring and analysis of APTs by providing a single, authoritative sequence of events that captures the context (and side effects) of potentially malicious activities. Provenance metadata allows a human analyst to backtrack from detection of malicious activity to the point of intrusion and, similarly, to work forward to fully understand the consequences. Applying provenance to APT monitoring and analysis introduces some significantly different challenges and requirements in comparison to more traditional applications. Drawing from our experiences working with and adapting the OPUS (Observed Provenance in User Space) system to an APT monitoring and analysis use case, we introduce and discuss some of the key challenges in this space. These preliminary observations are intended to prime a discussion within the community about the design space for scalable, efficient and trustworthy distributed provenance for scenarios that impose different constraints from traditional provenance applications such as workflow and data processing frameworks

General hardware multicasting for fine-grained message-passing architectures

Manycore architectures are increasingly favouring message-passing or partitioned global address spaces (PGAS) over cache coherency for reasons of power efficiency and scalability. However, in the absence of cache coherency, there can be a lack of hardware support for one-to-many communication patterns, which are prevalent in some application domains. To address this, we present new hardware primitives for multicast communication in rack-scale manycore systems. These primitives guarantee delivery to both colocated and distributed destinations, and can capture large unstructured communication patterns precisely. As a result, reliable multicast transfers among any number of software tasks, connected in any topology, can be fully offloaded to hardware. We implement the new primitives in a research platform consisting of 50K RISC-V threads distributed over 48 FPGAs, and demonstrate significant performance benefits on a range of applications expressed using a high-level vertex-centric programming model

Termination detection for fine-grained message-passing architectures

Barrier primitives provided by standard parallel programming APIs are the primary means by which applications implement global synchronisation. Typically these primitives are fully-committed to synchronisation in the sense that, once a barrier is entered, synchronisation is the only way out. For message-passing applications, this raises the question of what happens when a message arrives at a thread that already resides in a barrier. Without a satisfactory answer, barriers do not interact with message-passing in any useful way.In this paper, we propose a new refutable barrier primitive that combines with message-passing to form a simple, expressive, efficient, well-defined API. It has a clear semantics based on termination detection, and supports the development of both globally-synchronous and asynchronous parallel applications.To evaluate the new primitive, we implement it in a prototype large-scale message-passing machine with 49, 152 RISC-V threads distributed over 48 FPGAs. We show that hardware support for the primitive leads to a highly-efficient implementation, capable of synchronisation rates that are an order-of-magnitude higher than what is achievable in software. Using the primitive, we implement synchronous and asynchronous versions of a range of applications, observing that each version can have significant advantages over the other, depending on the application. Therefore, a barrier primitive supporting both styles can greatly assist the development of parallel programs. </p

A systematic review of older people's perceptions of facilitators and barriers to participation in falls-prevention interventions

Original article can be found at: http://journals.cambridge.org/ Copyright Cambridge University Press. DOI: 10.1017/S0144686X07006861The prevention of falls is currently high on the health policy agenda in the United Kingdom, which has led to the establishment of many falls-prevention services. If these are to be effective, however, the acceptability of services to older people needs to be considered. This paper reports a systematic review Of Studies of older people's perceptions of these interventions. The papers for review were identified by searching electronic databases, checking reference lists, and contacting experts. Two authors independently screened the studies and extracted data on the factors relating to participation in, or adherence to, falls-prevention strategies. Twenty-four studies were identified, of which 12 were qualitative. Only one study specifically examined interventions that promote participation in falls-prevention programmes; the others explored older people's attitudes and views. The factors that facilitated participation included social support, low intensity exercise, greater education, involvement in decision-making, and a perception of the programmes as relevant and life-enhancing. Barriers to participation included fatalism, denial and under-estimation of the risk of falling, poor self-efficacy, no previous history of exercise, fear of falling, poor health and functional ability, low health expectations and the stigma associated with programmes that targeted older people.Peer reviewe

Synthesis and biological evaluation of polysulfated oligosaccharide glycosides as inhibitors of angiogenesis and tumor growth

A series of polysulfated penta- and tetrasaccharide glycosides containing alpha(1 -> 3)/alpha(1 -> 2)-linked mannose residues were synthesized as heparan sulfate (HS) mimetics and evaluated for their ability to inhibit angiogenesis. The compounds bound lightly to angiogenic growth factors (FGF-1, FGF-2, and VEGF) and strongly inhibited heparanase activity. In addition, the compounds exhibited potent activity in cell-based and ex vivo assays indicative of angiogenesis, with tetrasaccharides exhibiting activity comparable to that of pentasaccharides. Selected compounds also showed good antitumor activity in vivo in a mouse melanoma (solid tumor) model resistant to the phase III HS mimetic 1 (muparfostat, formerly known as PI-88). The lipophilic modifications also resulted in reduced anticoagulant activity, a common side effect of HS mimetics, and conferred a reasonable pharmacokinetic profile in the rat, as exemplified by the sulfated octyl tetrasaccharide 5. The data support the further investigation of this class of compounds as potential antiangiogenic, anticancer therapeutics