Program activity graphs can be constructed from timestamped traces of appropriate execution events. tnfonnation about the activities on the k longest execution paths is useful in the analysis of parallel program perjiormance. In this papec four algorithms for finding the near-critical paths of program activity graphs are presented and compared, including an eflcient new algorithm that utilizes slack values calculated by the critical path method to perform a best-first search in linear space. The worst-case time and memory requirements of the new algorithm are in O(ke) and O(k+e), where e is the number of edges in the graph. Results confirming the eflciency of the algorithm are presented for five application programs. A framework for utilizing the near-critical path information is also described. The framework includes both statistical summaries and visualization capabilities.
A new multicomputer performance monitoring system is described in this paper. Where possible, the system employs portable performance monitoring instrumentation technology and leverages previous work. Trace event acquisition is hardware assisted and based on the MultiKron, a single-chip measurement solution developed at the National Institute for Standards and Technology. The user interface is based on the Pablo Performance Analysis Environment, a visualization and sonification toolkit developed at the University of Illinois. The SPIscope is introduced as a component that bridges the gap between these emerging standard interfaces. The SPIscope provides a high-bandwidth path to a large secondary storage for recording performance data. Connectivity to the user's performance analysis workstation is via a TCP/IP LAN. Facilities are provided to support application-specific trace events, breakpoint-style debugging, on-line transmission of selected data, and dynamic acquisition-rate control. By using existing technology and interfaces, we hope to contribute a performance monitoring component with greater utility throughout the parallel processing community.
The ATM Forum's LAN Emulation (LANE) Specification has now been available for more than two years, and LANE products have matured sufficiently that enterprises have deployed production LAN Emulation networks. However, the scaleability of LANE is still frequently debated, as is its applicability in Wide-Area Networks (WANs). This paper examines design features and supporting applications that can enhance the scaleability and manageability of LAN Emulation networks. The design features include techniques for distributing the LANE Services to provide load balancing and robustness, mechanisms for managing broadcast and multicast traffic (which have been a classical problem with large LAN networks), approaches for controlling signalling rates during power-up and failover situations, and extensions that exploit the distributed routing capabilities provided by the Next Hop Resolution Protocol (NHRP). Issues associated with WAN deployment of LAN Emulation are also explored, including requirements for canier-based service environments, where conservation of network resources, security capabilities, and monitoring applications are especially important. The paper is concluded with an assessment of LANE's status/prospects as a technology for building large-scale networks.
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