Marcin Lawenda

Scheduling multiple divisible loads in homogeneous star systems

Abstract In this paper we analyze scheduling multiple divisible loads on a star-connected system of identical processors. It is shown that this problem is computationally hard. Some special cases appear to be particularly difficult, so it is not even known if they belong to the class NP. Exponential algorithms and special cases solvable in polynomial time are presented.

Multi‐installment divisible load processing in heterogeneous distributed systems

Divisible loads are parallel applications with fine granularity and negligible data dependencies. Such computations can be divided into parts of arbitrary sizes and processed independently in parallel. The load distribution process incurs considerable communication delays. To reduce processor waiting time during the computation initialization phase, the load is distributed in multiple small installments rather than in one big chunk. In this paper we analyze multi‐installment divisible load processing in heterogeneous distributed systems. Scheduling divisible loads in heterogeneous systems is hard because the sizes of the installments should be adjusted to the communication and computation capabilities of the system. We show that ignoring heterogeneity of the distributed system may result in arbitrarily bad solutions. Two algorithms are proposed to gear the load chunk sizes to different communication and computation speeds: an optimization branch‐and‐bound algorithm and a heuristic based on a genetic search method. The running times of both methods and the quality of the solutions are compared. Then, we use these algorithms to study the features of the multi‐installment divisible load scheduling problem. We demonstrate that it has both combinatorial and algebraic nature, and that optimum solutions are harder to find with the growing heterogeneity of the system. Copyright

Virtual Laboratory as a Remote and Interactive Access to the Scientific Instrumentation Embedded in Grid Environment

The following paper describes the key architecture elements of the Virtual Laboratory Project, which is developed in the Poznan Supercomputing and Networking Center. Project started in 2002, and since then the work was carried under different statesponsored grants and now is carried under EU FP6 IST projects. The authors will explain briefly the main ideas and key design elements behind this original concept. The current state of the project will be presented, as the project reached its production phase, and plans for the near and far future will be revealed. A special attention will be given to the concept and implementation of Digital Science Library, as it plays an important role in the scope of the whole system. Although the various aspects of this system were presented on workshops and conferences, this paper brings together all the pieces, and presents the overall look on the entire scope of this Virtual Laboratory System.

On optimum multi-installment divisible load processing in heterogeneous distributed systems

In this paper we study multi-installment divisible load processing in heterogeneous distributed systems. Divisible loads are computations which can be divided into parts of arbitrary sizes, and these parts can be processed independently in parallel. In order to reduce the waiting time during the parallel computation initialization phase, load is sent to the processors in multiple small installments. In a heterogeneous system the sizes of the installments should be adjusted to the communication, and computation capabilities of the processors. We propose two algorithms that gear the load chunk sizes to different communication and computation speeds. The first one is an optimization branch and bound algorithm. The second algorithm is based on genetic search. The running times of both methods and the quality of the genetic algorithm solutions are compared. Then, we use these algorithms to analyze features of the scheduling problem solutions.

Multi-installment divisible load processing in heterogeneous systems with limited memory

Optimum divisible load processing in heterogeneous star system with limited memory is studied. We propose two algorithms to find multi-installment load distribution: Exact branch-and-bound algorithm and a heuristic using genetic search method. Characteristic features of the solutions and the performance of the algorithms are examined in a set of computational experiments.

Scheduling Multiple Divisible Loads

In this paper we study the scheduling of multiple divisible loads on a star network of processors. We show that this problem is computationally hard. Special cases solvable in polynomial time are identified.

Experimental study of scheduling with memory constraints using hybrid methods

In this paper we study divisible load scheduling in systems with limited memory. Divisible loads are parallel computations which can be divided into independent parts processed in parallel on remote computers, and the part sizes may be arbitrary. The distributed system is a heterogeneous single level tree. The total size of processor memories is too small to accommodate the whole load at any moment of time. Therefore, the load is distributed in many rounds. Memory reservations have block nature. The problem consists in distributing the load taking into account communication time, computation time, and limited memory buffers so that the whole processing finishes as early as possible. This problem is both combinatorial and algebraic in nature. Therefore, hybrid algorithms are given to solve it. Two algorithms are proposed to solve the combinatorial component. A branch-and-bound algorithm is nearly unusable due to its complexity. Then, a genetic algorithm is proposed with more tractable execution times. For a given solution of the combinatorial part we formulate the solution of the algebraic part as a linear programming problem. An extensive computational study is performed to analyze the impact of various system parameters on the quality of the solutions. From this we were able to infer on the nature of the scheduling problem.

A new model of multi-installment divisible loads processing in systems with limited memory

In this paper we study multi-installment divisible load processing in a heterogeneous distributed system with limited memory. Divisible load model applies to computations which can be arbitrarily divided into parts and performed independently in parallel. The initial waiting for the load may be shortened by sending many small chunks of load instead of one huge. The load chunk sizes must be adjusted to the speeds of communication, computation, and memory sizes, such that the whole processing time is as short as possible. We propose a new realistic model of memory management, and formulate it as mixed quadratic programming problem which is solved by branch and bound algorithm. Since this problem is computationally hard we propose heuristics, and analyze their performance in a series of computational experiments.

Remote Instrumentation for eScience and Related Aspects

This book will focus on new Remote Instrumentation aspects related to middleware architecture, high-speed networking, wireless Grid for acquisition devices and sensor networks, QoS provisioning for real-time control, measurement instrumentation and methodology. Moreover, it will provide knowledge about the automation of mechanisms oriented to accompanying processes that are usually performed by a human. Another important point of this book is focusing on the future trends concerning Remote Instrumentation systems development and actions related to standardization of remote instrumentation mechanisms.

Software VLBI correlator - Practical approach

In the paper authors present the general idea of software correlator in e-VLBI system. The e-VLBI idea is undoubtedly the future of radio astronomy which allows accelerate both measurement and post-processing procedures. Software correlation idea is a new approach to the space observation base on very long baseline interferometry method. It significantly reduces processing time of obtained data from 6 months up to few minutes so the scientists can almost immediately familiarize with results of their tests. That is why finding (sub)optimal solutions for designing and working of software correlator is essential for radio astronomy society. The paper touches many important and up-to-date aspects from e-VLBI domain including preparation phase to the correlation process. Moreover, experimental results are presented concerning different aspects of data availability which proof that quasi real time software correlation process is possible.