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Abstract-Currently deployed grids gather together thousands of computational and storage resources for the benefit of a large community of scientists. However, the large scale, the wide geographical spread, and at times the decision of the rightful resource owners to commit the capacity elsewhere, raises serious resource availability issues. Little is known about the characteristics of the grid resource availability, and of the impact of resource unavailability on the performance of grids. In this work, we make first steps in addressing this twofold lack of information. First, we analyze a long-term availability trace and assess the resource availability characteristics of Grid'5000, an experimental grid environment of over 2,500 processors. The average utilization for the studied trace is increased by almost 5%, when availability is considered. Based on the results of the analysis, we further propose a model for grid resource availability. Our analysis and modeling results show that grid computational resources become unavailable at a high rate, negatively affecting the ability of grids to execute long jobs. Second, through trace-based simulation, we show evidence that resource availability can have a severe impact on the performance of the grid systems. The results of this step show evidence that the performance of a grid system can rise when availability is taken into consideration, and that human administration of availability change information results in 10-15 times more job failures than for an automated monitoring solution, even for a lowly utilized system.

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Abstract-The arrival of the P2P model has opened many new avenues for research within the field of distributed computing. This is mainly due to important practical features (such as support for volatility, high scalability). Several generic P2P libraries have been proposed for building higher-level services. In order to judge the appropriateness of using a generic P2P library for a given application type, an experimental performance evaluation of the provided functionalities is unavoidable. Very few analyses of this kind have been reported, as most evaluations are limited to complexity analyses and to simulations. Such experimental analyses are important, especially when using P2P software in a grid computing context, where applications may have precise efficiency requirements. In this paper, we focus on JXTA, which provides generic building blocks and protocols intended to serve as a basis for specialized P2P services and applications. We perform a performance evaluation of the three communication layers (endpoint, pipe and socket) over a Fast Ethernet local-area network, for recent versions of the J2SE and C bindings of JXTA. We provide a detailed analysis explaining the behavior of these three layers and we give hints showing how to efficiently use them.

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Many-core architectures are promising hardware to design real-time systems. However, the worst-case behavior of the Network-on-Chip (NoC) for both core-to-core and core-to-Input/Output 1 (I/O) communications of critical applications must be established. The mapping over the NoC of both critical and non-critical applications has an impact on the network contention these critical communications exhibit. So far, all existing mapping strategies have focused on core-to-core communications. However, many-cores in embedded real-time systems will be integrated within backbone Ethernet networks, as they mostly provide Ethernet controllers as I/O interfaces. In a previous work we have shown that Ethernet packets can be dropped due to an internal congestion in a Tilera-like NoC. In this work, we describe and evaluate a mapping strategy for such Tilera-like NoCs that minimizes the contention of core-to-I/O critical flows in order to solve this problem. Experimental results on real avionics applications show significant improvements of coreto-IO flows transmission delays, without significantly impacting transmission delays of core-to-core flows.