14547983
Evaluating Hardware Support for Reference Counting Using Software Configurable Processors
Reference counting is an incremental garbage collection technique that yields nearly unnoticeable pause time but can suffer from high processing overhead. Previous attempts to use hardware to reduce this overhead have shown successes but limited applicability. With recent discovery that reference counting can be well suited for Java embedded devices, it is worthwhile to rethink hardware solutions that can further improve its performance by leveraging current trends in embedded computing. In this paper, we introduce a custom instruction solution that is (i) more practical because it only provides hardware support for the expensive but straight-forward software function-reference count update; the existing complex runtime functions such as memory allocation and liberation remain unchanged and (ii) better positioned for widespread adoption because it is designed to leverage readily available configurable logics in many embedded processor cores. As a proof-of-concept, we implement two reference counting algorithms that utilize the proposed custom instructions on Stretch S5000 software reconfigurable processors. We then analyze the performance impacts on the execution time as well as the architectural behavior. The results show that we can achieve as much as 70% performance gain over pure software implementation.
9864742
JOPI: a Java object-passing interface
Recently there has been an increasing interest in developing parallel programming capabilities in Java to harness the vast resources available in clusters, grids and heterogeneous networked systems. In this paper, we introduce a Java object-passing interface (JOPI) library. JOPI provides Java programmers with the necessary functionality to write object-passing parallel programs in distributed heterogeneous systems. JOPI provides an MPI-like interface that can be used to exchange objects among processes. In addition to the well-known benefits of the object-oriented development model, using objects to exchange information in JOPI is advantageous because it facilitates passing complex structures and enables the programmer to isolate the problem space from the parallelization problem. The run-time environment for JOPI is portable, efficient and provides the necessary functionality to deploy and execute parallel Java programs. Experiments were conducted on a cluster system and a collection of heterogeneous platforms to measure JOPI's performance and compare it with MPI. The results show good performance gains using JOPI.
8918525
An efficient, low-cost inconsistency detection framework for data and service sharing in an Internet-scale system
In this paper, we argue that a broad range of Internet-scale distributed applications can benefit from an underlying low-cost consistency detection framework that is an alternative to inconsistency avoidance and can detect inconsistency among nodes sharing data or services in a timely manner. This paper first presents an overview of the inconsistency detection framework. Then, it discusses the detailed design of the two-layer inconsistency detection module, the core component of this framework, which can detect inconsistency among nodes in a timely manner. The proposed two-layer inconsistency detection module is evaluated both analytically and via simulations, which shows that this module can significantly reduce the time to detect inconsistency among nodes without adding much maintenance cost. Finally, this paper outlines the possible mechanisms to discern the application semantics and to resolve the detected inconsistencies
16880603
Adaptive Load Balancing for Long-Range MD Simulations in A Distributed Environment
Molecular dynamics, a computationally intensive application is used by researchers in various fields. The inherent parallelism (Plimpton and Hendrickson, 1994) in the computations involved with this application can be exploited in parallel and distributed environments. However, in distributed environments such as the grid (Foster et al., 2001), the available resources, namely the network and computational power, are continually changing with respect to every available node. To optimally utilize these dynamic resources, a scheduler should be able to continually adapt to the changes and suitably vary the load scheduled to every available node. We propose one such scheduling algorithm. The proposed scheduling algorithm builds and continually updates a model of the distributed system, which it then uses to make decisions about how to optimally redistribute the load in the system at every time step of the MD simulation. The scheduling algorithm can additionally handle dynamic changes in the number of nodes available for computation at runtime. We then demonstrate the efficiency of our scheduling algorithm when applied to MD simulations in a distributed environment
1546029
Design and Analysis of Hierarchical Ring Networks for Shared-Memory Multiprocessors
ÐWe study four augmentations of ring networks which are intended to enhance a ring's efficiency as a communication medium significantly, while increasing its structural complexity only modestly. Chordal rings add ashortcuto edges, which can be viewed as chords, to the ring. Express rings are chordal rings whose chords are routed outside the ring. Multirings append subsidiary rings to edges of a ring and, recursively, to edges of appended subrings. Hierarchical ring networks (HRN's) append subsidiary rings to nodes of a ring and, recursively, to nodes of appended subrings. We show that these four modes of augmentation are very closely related: 1) Planar chordal rings, planar express rings, and multirings are topologically equivalent families of networks with the acutwidtho of an express ring translating into the atree deptho of its isomorphic multiring and vice versa. 2) Every depth-d HRN is a spanning subgraph of a depth-2dÿ 1 multiring. 3) Every depth-d multiring M can be embedded into a d-dimensional mesh with dilation 3 in such a way that some node of M resides at a corner of the mesh. 4) Every depth-d HRN H can be embedded into a d-dimensional mesh with dilation 2 in such a way that some node of H resides at a corner of the mesh. In addition to demonstrating that these four augmented ring networks are grid graphs, our embedding results afford us close bounds on how much decrease in diameter is achievable for a given increase in structural complexity for the networks. Specifically, we derive upper and lower bounds on the optimal diameters of N-node depth-d multirings and HRNs that are asymptotically tight for large N and d. Index TermsÐRing networks, chordal rings, express rings, multirings, hierarchical ring networks, grid graphs, graph embedding, diameter trade-offs.
26735928
I/O Response Time in a Fault-Tolerant Parallel Virtual File System
A fault tolerant parallel virtual file system is designed and implemented to provide high I/O performance and high reliability. A queuing model is used to analyze in detail the average response time when multiple clients access the system. The results show that I/O response time is with a function of several operational parameters. It decreases with the increase in I/O buffer hit rate for read requests, write buffer size for write requests and number of server nodes in the parallel file system, while higher I/O requests arrival rate increases I/O response time.
14525964
Adaptive strategies for efficiently locating internet-based servers in MANETs
Providing Internet access to Mobile Ad hoc Networks (MANETs) can greatly extend their applications, increase their scalability, and improve the quality of service. However, a critical problem is how the mobile hosts can locate Internet-based servers efficiently in a dynamic, unstructured network. Neither reactive strategies, where the hosts initiate on-demand server discovery, nor proactive strategies, where the servers periodically advertise their availability information, are optimal. To that end, this paper studies adaptive strategies that (1) combine both proactive advertising by the servers and on-demand discovery by the mobile hosts, and (2) determine the relative rate of proactive advertising and on-demand discovery adaptively according to the network characteristics including the host mobility level and the offered load. We propose and evaluate two novel, integrated algorithms. First, to determine the rate of proactive advertising, we propose an exponential backoff algorithm to probe the optimal operating point. Second, to reduce the network traffic due to reactive (on-demand) discovery, we propose a novel controlled flooding algorithm. Our simulation study reveals that, compared to the previous proactive strategies and reactive strategies, our adaptive strategies reduce network traffic for locating the servers by several times when the network has a moderate offered load and a low or high level of host mobility.
20921565
Dynamical Process of Excitation Fusion in Polymers
Due to the confinement effect in the nondegenerate polymers and the electron-lattice interaction, the electron-hole pair forms a self-trapped single excitation. It is shown that two single excitations in one chain can fuse into one double excitation, and the relaxation time of the fusion process is about 160 fs.
16310485
Stably Computable Properties of Network Graphs
We consider a scenario in which anonymous, finite-state sensing devices are deployed in an ad-hoc communication network of arbitrary size and unknown topology, and explore what properties of the network graph can be stably computed by the devices. We show that they can detect whether the network has degree bounded by a constant d, and, if so, organize a computation that achieves asymptotically optimal linear memory use. We define a model of stabilizing inputs to such devices and show that a large class of predicates of the multiset of final input values are stably computable in any weakly-connected network. We also show that nondeterminism in the transition function does not increase the class of stably computable predicates.
18487363
Confidence measures for speech recognition: A survey
Abstract In speech recognition, confidence measures (CM) are used to evaluate reliability of recognition results. A good confidence measure can largely benefit speech recognition systems in many practical applications. In this survey, I summarize most research works related to confidence measures which have been done during the past 10–12 years. I will present all these approaches as three major categories, namely CM as a combination of predictor features, CM as a posterior probability, and CM as utterance verification. Then, I also introduce some recent advances in the area. Moreover, I will discuss capabilities and limitations of the current CM techniques and generally comment on today’s CM approaches. Based on the discussion, I will conclude the paper with some clues for future works.
18051966
Design and analysis of adaptive strategies for locating internet-based servers in MANETs
A critical problem in providing Internet access to Mobile Ad Hoc Networks (MANETs) is how the mobile hosts can locate Internet-based servers efficiently in a dynamic, unstructured network. This paper studies adaptive strategies that combine both proactive advertising by the servers and on-demand discovery by the mobile hosts. The adaptive strategies determine the relative rate of proactive advertising and on-demand discovery according to system characteristics such as host mobility level and offered load. Our simulation study reveals that, compared to the previous proactive strategies and reactive strategies, the adaptive strategies reduce network traffic by several times when the network has a moderate offered load and a low or high level of host mobility.