Kamil Iskra

The distributed ASCI Supercomputer project

The Distributed ASCI Supercomputer (DAS) is a homogeneous wide-area distributed system consisting of four cluster computers at different locations. DAS has been used for research on communication software, parallel languages and programming systems, schedulers, parallel applications, and distributed applications. The paper gives a preview of the most interesting research results obtained so far in the DAS project.

The implementation of dynamite: an environment for migrating PVM tasks

Parallel programming on clusters of workstations is increasingly attractive, but dynamic load balancing is needed to make efficient use of the available resources. Dynamite provides dynamic load balancing for PVM applications running under Linux and Solaris. It supports migration of individual tasks between nodes in a manner transparent both to the application programmer and to the user, implemented entirely in user space. Dynamically linked executables are supported, as are tasks with open files and with direct PVM connections. In this paper, we describe the technical aspects of migrating message-passing tasks.

The Polder Computing Environment: a system for interactive distributed simulation

The paper provides an overview of an experimental, Grid‐like computing environment, Polder, and its components. Polder offers high‐performance computing and interactive simulation facilities to computational science. It was successfully implemented on a wide‐area cluster system, the Distributed ASCI Supercomputer. An important issue is an efficient management of resources, in particular multi‐level scheduling and migration of tasks that use PVM or sockets. The system can be applied to interactive simulation, where a cluster is used for high‐performance computations, while a dedicated immersive interactive environment (CAVE) offers visualization and user interaction. Design considerations for the construction of dynamic exploration environments using such a system are discussed, in particular the use of intelligent agents for coordination. A case study of simulatedabdominal vascular reconstruction is subsequently presented: the results of computed tomography or magnetic resonance imaging of a patient are displayed in CAVE, and a surgeon can evaluate the possible treatments by performing the surgeries virtually and analysing the resulting blood flow which is simulated using the lattice‐Boltzmann method. Copyright

Toward Grid-Aware Time Warp

The authors study the adaptation of an optimistic Time Warp kernel to cross-cluster computing on the Grid. Wide-area communication, the primary source of overhead, is offloaded onto dedicated routing processes. This allows the simulation processes to run at full speed and thus significantly decreases the performance gap caused by the wide-area distribution. Further improvements are obtained by employing message aggregation on the wide-area links and using a distributed global virtual time algorithm. The authors achieve many of their objectives for a cellular automaton simulation with lazy cancellation and moderate communication. High communication rates, especially with aggressive cancellation, present a challenge. This is confirmed by the experiments with synthetic loads. Even then, a satisfactory speedup can be achieved, provided that the computational grain of events is large enough.

Time Warp cancellation optimizations on high latency networks

We investigate the performance of the time warp kernel APSIS when running on various communication layers, in particular on a wide-area grid. Several cancellation strategies are tried, among them the lazy cancellation and a little known bulk anti-messages optimization. Our experiments with an Ising spin simulation indicate that the slowdown caused by high latency networks, while significant, is not catastrophic; and that it can be significantly reduced using the lazy cancellation. Experiments suggest that further improvements can be expected if a more elaborate communication infrastructure is put in place.

Experiments with Migration of Message-Passing Tasks

The combined computing capacity of the workstations that are present in many organisations nowadays is often under-utilised, as the performance for parallel programs is unpredictable. Load balancing through dynamic task re-allocation can help to obtain a more reliable performance. The Esprit project Dynamite provides such an automated load balancing system. It can migrate tasks that are part of a parallel program using a message passing library. Currently Dynamite supports PVM only, but it is being extended to support MPI as well. The Dynamite package is completely transparent, i.e. neither system (kernel) nor application source code need to be modified. Dynamite supports migration of tasks using dynamically linked libraries, open files and both direct and indirect PVM communication. Monitors and a scheduler are included. In this paper, we first briefly describe the Dynamite system. Next we describe how migration decisions are made and report on some performance measurements.

Parallel implementation of a cellular automaton model for the simulation of laser dynamics

The classical modeling approach for laser study relies on the differential equations. In this paper, a cellular automaton model is proposed as an alternative for the simulation of population dynamics. Even though the model is simplified it captures the essence of laser phenomenology: (i) there is a threshold pumping rate that depends inversely on the decaying lifetime of the atoms and the photons; and (ii) depending on these lifetimes and on the pumping rate, a constant or an oscillatory behavior can be observed. More complex behaviors such as spiking and pattern formation can also be studied with the cellular automaton model.

Enhancing the Functionality of Performance Measurement Tools for Message Passing Environments

The paper presents the concept of and insight into enhancing the portability and functionality of two performance measurement tools - PATOP and TATOO - in order to adapt them to work with message passing applications. We discuss the concepts of porting the tools to the OCM monitoring environment, the structure of the modified tools and the extensions made, as well as implementation issues.

Performance Measurements on Dynamite/DPVM

The total computing capacity of workstations can be harnessed more efficiently by using a dynamic task allocation system. The Esprit project Dynamite provides such an automated load balancing system, through the migration of tasks of a parallel program using PVM. The Dynamite package is completely transparent, i.e. neither system (kernel) nor application program modifications are needed. Dynamite supports migration of tasks using dynamically linked libraries, open files and both direct and indirect PVM communication. In this paper we briefly introduce the Dynamite system and subsequently report on a collection of performance measurements.

Performance analysis of a parallel discrete model for the simulation of laser dynamics

This paper presents an analysis on the performance of a parallel implementation of a discrete model of laser dynamics, which is based on cellular automata. The performance of a 2D parallel version of the model is studied as a first step to test the feasibility of a parallel 3D version, which is needed to simulate specific laser systems. The 3D version will have to run on a parallel computer due to its runtime and memory requirements. The model has been implemented on a Beowulf cluster using the message passing paradigm. The parallel implementation is found to exhibit a good speedup, allowing us to run realistic simulations of laser systems on clusters of workstations, which could not be afforded on an individual machine due to the extensive runtime and memory size needed