优化机器人多处理机控制系统性能方法

分析了有腿的步行机器人控制器性能瓶颈的产生原因.提出优化机器人多处理机控制系统性能的有效方法。     

Metadata-driven optimal transcoding in a multimedia proxy

An adaptive multimedia proxy is presented which provides (1) caching, (2) filtering, and (3) media gateway functionalities. The proxy can perform media adaptation on its own, either relying on layered coding or using transcoding mainly in the decompressed domain. A cost model is presented which incorporates user requirements, terminal capabilities, and video variations in one formula. Based on this model, the proxy acts as a general broker of different user requirements and of different video variations. This is a first step towards What You Need is What You Get (WYNIWYG) video services, which deliver videos to users in exactly the quality they need and are willing to pay for. The MPEG-7 and MPEG-21 standards enable this in an interoperable way. A detailed evaluation based on a series of simulation runs is provided.     

基于网络光盘库的Cache替换算法

Cache作为提高访问效率、改善系统性能的重要环节和技术，广泛地应用于各种计算、匹配场合中。除了在处理器上使用之外，在Web访问及存储系统中，为了提高访问速度，Cache也扮演了重要的角色。该文分析了当前应用于处理器、Web Cache等方面的替换算法，针对网络光盘库这个存储系统的自身特点，提出了一种新的替换算法。该算法结合了LFU和MQ这两种算法的特点，提高了数据在Cache中的命中率。实验表明替换算法与访问模型密切相关。     

无线Ad Hoc网络P2P流媒体分发缓存算法

无线Ad Hoc网络由于其传输时延较长,网络拓扑动态变化以及高丢包率,给流媒体在无线网络中的分发带来了挑战.但随着移动通信终端设备存储能力的提高,在无线Ad Hoc网络中进行P2P的流媒体分发服务成为可能.本文提出一种最小化网络总体有效传输代价的P2P流媒体分发启发式缓存算法,它是在网络总体缓存资源有限的条件下,综合考虑流媒体片段内部流行度、无线节点可靠性,以及片段实际缓存密度与期望缓存密度之差等因素,以减少流媒体分发总体传输代价为目标的启发式缓存算法,此算法能很好地减少流媒体分发起动时延,有效地减少流媒体分发在无线Ad Hoc网络中的传输代价.     

Timing predictability of cache replacement policies

Hard real-time systems must obey strict timing constraints. Therefore, one needs to derive guarantees on the worst-case execution times of a system’s tasks. In this context, predictable behavior of system components is crucial for the derivation of tight and thus useful bounds. This paper presents results about the predictability of common cache replacement policies. To this end, we introduce three metrics, evict, fill, and mls that capture aspects of cache-state predictability. A thorough analysis of the LRU, FIFO, MRU, and PLRU policies yields the respective values under these metrics. To the best of our knowledge, this work presents the first quantitative, analytical results for the predictability of replacement policies. Our results support empirical evidence in static cache analysis.

A window-assisted video partitioning strategy for partitioning and caching video streams in distributed multimedia systems

In this paper, we address the issue of efficiently streaming a set of heterogenous videos under the constraint of service latency over a scalable multimedia systems. We propose a novel strategy, referred to as window-assisted video partitioning (WAVP), for rendering cost-effective multimedia services. The objective is to minimize the service cost and maximize the number of requests that can be successfully served under resources constraints (cache capacity and link bandwidth). We formulate the problem of video partitioning as an optimization of both bandwidth resources and cache space, and derive the optimal schedule window for different video portions under consideration of time constraints, the popularities and the sizes of the video portions. In WAVP, video are partitioned into multiple portions and delivered according to by adaptive schedule windows. We prove that WAVP strategy not only optimize the service cost but also be able to serve requests under the time constraints without causing too much delay. We conduct mathematical analysis and derive certain performance bounds that quantify the overall performance of the strategy. It shows that the service cost can be optimized by adjusting the schedule window and resources utilization can be improved as video streams are partitioned into multiple portions. We evaluate the performance under several influencing parameters such as available bandwidth, cache capacity, and partition gradients. Simulation results show that our proposed method can not only significantly reduce the service cost under tight time constraints and with low partition overhead, but also balance the utilization of network resources to achieve high acceptance ratio with low average service cost.     

局域网流媒体Caching代理服务器的实现

With the widespread use of streaming media application on the Internet, a significant change in Internet workload will be provoked.Caching is one kind of applied technique relatively for enhancing the scalability of streaming system and reducing the workload of server/network. We have utilized RTP/RTSP protocol, and implemented the prototype of streaming proxy caching based on LAN in visual C-t-t-environment with WINSOCK network interface. This system can play a role in decreasing server load, reducing the traffic from streaming server to proxy, and improving the Start-up latency of the client.     

并行视频服务器磁盘Cache策略研究

文章分析了并行VOD系统的系统结构,对并行视频服务器中的磁盘Cache技术进行了深入的探讨,提出了一种磁盘Cache替换算法PLFU(PeriodLeastFrequentlyUsed),并成功地应用在笔者开发的并行视频服务器中。     

多级缓存模式下的数据块替换优化算法

多数处理器中采用多级包含的cache存储层次,现有的末级cache块替换算法带来的性能开销较大.针对该问题,提出一种优化的末级cache块替换算法PLI,在选择丢弃块时考虑其在上级cache的访问频率,以较小的代价选出最优的LLC替换块.在时钟精确模拟器上的评测结果表明,该算法较原算法性能平均提升7％.     

An initial evaluation of the Convex SPP-1000 for earth and space science applications

The Convex SPP-1000 is the most recent of the new generation of Scalable Parallel Computing systems being offered commercially. The SPP-1000 is distinguished by incorporating the first commercial version of directory based cache coherence mechanisms and the emerging Scalable Coherent Interface protocol to achieve a true global shared memory capability. Pairs of HP PA-RISC processors are combined in clusters of 8 processors using a cross-bar switch. Up to 16 clusters are interconnected using 4 ring networks in parallel with a distributed global cache. To evaluate this new system in a Beta test environment, the Goddard Space Flight Center conducted three classes of operational experiments with an emphasis on applications related to Earth and space science. A cluster was tested as a platform for executing a multiple program workload exploiting job-stream level parallelism. Synthetic programs were run to measure overhead costs of barrier, fork-join, and message passing synchronization primitives. A key problem for Earth and space science studies is gravitational N-body simulation of solar systems to galactic clusters. An efficient tree-code version of this problem was run to reveal scaling properties of the system and to measure the overall efficiency. This paper presents the experimental results and findings of this study and provides the earliest published evaluation of this new scalable architecture.