Philip K. McKinley

A survey of wormhole routing techniques in direct networks

Several research contributions and commercial ventures related to wormhole routing, a switching technique used in direct networks, are discussed. The properties of direct networks are reviewed, and the operation and characteristics of wormhole routing are discussed in detail. By its nature, wormhole routing is particularly susceptible to deadlock situations, in which two or more packets may block one another indefinitely. Several approaches to deadlock-free. routing, along with a technique that allows multiple virtual channels to share the same physical channel, are described. In addition, several open issues related to wormhole routing are discussed.<<ETX>>

Composing adaptive software

Interest in adaptive computing systems has increased dramatically in the past few years, and a variety of techniques now allow software to adapt dynamically to its environment. Compositional adaptation enables software to modify its structure and behavior dynamically in response to change in its execution environment. A review of current technology compares how, when, and where recomposition occurs.

Unicast-based multicast communication in wormhole-routed networks

Multicast communication, in which the same message is delivered from a source node to an arbitrary number of destination nodes, is being increasingly demanded in parallel computing. System supported multicast services can potentially offer improved performance, increased functionality, and simplified programming, and may in turn be used to support various higher-level operations for data movement and global process control. This paper presents efficient algorithms to implement multicast communication in wormhole-routed direct networks, in the absence of hardware multicast support, by exploiting the properties of the switching technology. Minimum-time multicast algorithms are presented for n-dimensional meshes and hypercubes that use deterministic, dimension-ordered routing of unicast messages. Both algorithms can deliver a multicast message to m-1 destinations in [log/sub 2/ m] message passing steps, while avoiding contention among the constituent unicast messages. Performance results of implementations on a 64-node nCUBE-2 hypercube and a 168-node Symult 2010 2-D mesh are given. >

Deadlock-free multicast wormhole routing in 2-D mesh multicomputers

Multicast communication services, in which the same message is delivered from a source node to an arbitrary number of destination nodes, are being provided in new-generation multicomputers. Broadcast is a special case of multicast in which a message is delivered to all nodes in the network. The nCUBE-2, a wormhole-routed hypercube multicomputer, provides hardware support for broadcast and a restricted form of multicast in which the destinations form a subcube. However, the broadcast routing algorithm adopted in the nCUBE-2 is not deadlock-free. In this paper, four multicast wormhole routing strategies for 2-D mesh multicomputers are proposed and studied. All of the algorithms are shown to be deadlock-free. These are the first deadlock-free multicast wormhole routing algorithms ever proposed. A simulation study has been conducted that compares the performance of these multicast algorithms under dynamic network traffic conditions in a 2-D mesh. The results indicate that a dual-path routing algorithm offers performance advantages over tree-based, multipath, and fixed-path algorithms. >

Collective communication in wormhole-routed massively parallel computers

Most MPC networks use wormhole routing to reduce the effect of path length on communication time. Researchers have exploited this by designing ingenious algorithms to speed collective communication. Many projects have addressed the design of efficient collective communication algorithms for wormhole-routed systems. By exploiting the relative distance-insensitivity of wormhole routing, these new algorithms often differ fundamentally from their store-and-forward counterparts. We examine software and hardware approaches to implementing collective communication operations. Although we emphasize methods in which the underlying architecture is a direct network, such as a hypercube or mesh, as opposed to an indirect switch-based network, several approaches apply to systems of either type. We illustrate several issues arising in this research area and describe the major classes of algorithms proposed to solve these problems.

The message flow model for routing in wormhole-routed networks

In this paper, we introduce a new approach to deadlock-free routing in wormhole-routed networks called the message flow model. This method may be used to develop deterministic, partially-adaptive, and fully-adaptive routing algorithms for wormhole-routed networks with arbitrary topologies. We first establish the necessary and sufficient condition for deadlock free routing, based on the analysis of the message flow on each channel. We then use the model to develop new adaptive routing algorithms for 2D meshes. >

An aspect-oriented approach to dynamic adaptation

This paper presents an aspect-oriented approach to dynamic adaptation. A systematic process for defining where, when, and how an adaptation is to be incorporated into an application is presented. Specifically, the paper presents a two-phase approach to dynamic adaptation, where the first phase prepares a non-adaptive program for adaptation, and the second phase implements the adaptation at run time. This approach is illustrated with a distributed conferencing application.

Efficient implementation of barrier synchronization in wormhole-routed hypercube multicomputers☆

Abstract Efficient implementation of barrier synchronization is important to the performance of many parallel algorithms. This paper addresses barrier synchronization in wormhole-routed hypercube multicomputers. A broadcast barrier involves all nodes in a system, whereas the more general multicast barrier involves an arbitrary subset of nodes. Although performance of barrier synchronization can benefit from hardware-supported broadcast and multicast operations, many systems support only single-destination, or unicast, communication in hardware. For such systems, a novel software tree approach, the U-cube tree, is proposed as the basis of barrier synchronization. An important feature of the U-cube tree is that all messages injected into the network are guaranteed to be contention-free. Performance measurements of several barrier synchronization techniques implemented on a 64-node nCUBE-2 are given.

TRAP/J: Transparent Generation of Adaptable Java Programs

This paper describes TRAP/J, a software tool that enables new adaptable behavior to be added to existing Java applications transparently (that is, without modifying the application source code and without extending the JVM). The generation process combines behavioral reflection and aspect-oriented programming to achieve this goal. Specifically, TRAP/J enables the developer to select, at compile time, a subset of classes in the existing program that are to be adaptable at run time. TRAP/J then generates specific aspects and reflective classes associated with the selected classes, producing an adapt-ready program. As the program executes, new behavior can be introduced via interfaces to the adaptable classes. A case study is presented in which TRAP/J is used to introduce adaptive behavior to an existing audio-streaming application, enabling it to operate effectively in a lossy wireless network by detecting and responding to changing network conditions.

The Message Flow Model for Routing in Wormhole-Routed Networks

In this paper, we introduce a new approach to deadlock-free routing in wormhole-routed networks called the message flow model. We first establish the necessary and sufficient condition for deadlock-free routing based on the analysis of the message flow on each channel. We then show how to use the model to prove that a given adaptive routing algorithm is deadlock-free. Finally, we use the method to de¿ velop new, efficient adaptive routing algorithms for 2D meshes and hypercubes.