Chi-Chung Hui

Improved strategies for dynamic load balancing

The authors propose two strategies for dynamic load balancing: one takes network delay into account to avoid errors in scheduling jobs; the other also delays job execution when the system is fully used. These strategies are general and can augment existing algorithms.

Hydrodynamic load balancing

This paper presents a hydrodynamic framework to solving the dynamic load balancing problem in heterogeneous distributed systems. In this approach, each processor is viewed as a liquid cylinder where the cross-sectional area corresponds to the capacity of the processor, the communication links are modeled as liquid channels between the cylinders, the workload is represented by liquid, and the load balancing algorithm manages the flow of the liquid. It is proven that all algorithms under this framework converge geometrically to the state of equilibrium, in which the heights of the liquid columns are the same in all the cylinders. In this way, each processor obtains an amount of workload proportional to its capacity. A hydrodynamic algorithm is presented and its performance is evaluated. The algorithm is applied to solve several practical applications to demonstrate the applicability of the framework.

Allocating task interaction graphs to processors in heterogeneous networks

The problem of allocating task interaction graphs (TIGs) to heterogeneous computing systems to minimize job completion time is investigated. The only restriction is that the interprocessor communication cost is the same for any pair of processors. This is suitable for local area network based systems, such as Ethernet, as well as fully interconnected multiprocessor systems. An optimal polynomial solution exists if sufficient homogeneous processors and communication capacity are available. This solution is generalized to obtain two faster heuristics, one for the case of homogeneous processors and the other for heterogeneous processors. The heuristics were tested extensively with 60,900 systematically generated random TIGs and shown to be stable independent of the size of the TIG. A performance model is also proposed to predict the performance of the heuristic algorithms, and it is successful in explaining the experimental results qualitatively.

Theoretical Analysis of the Heterogeneous Dynamic Load-Balancing Problem Using a Hydrodynamic Approach

This paper presents a hydrodynamic framework for solving the dynamic load-balancing problem on a network of heterogeneous computers. In this approach, each processor is viewed as a liquid cylinder where the cross-sectional area corresponds to the capacity of the processor, the communication links are modeled as liquid channels between the cylinders, the workload is represented as liquid, and the load-balancing algorithm describes the flow of the liquid. It is proven that all algorithms under this framework converge geometrically to the state of equilibrium, in which the heights of the liquid columns are the same in all the cylinders. In this way, each processor obtains an amount of workload proportional to its capacity. The parameters that affect the convergence rates of the algorithms are also identified and discussed.

A hydro-dynamic approach to heterogeneous dynamic load balancing in a network of computers

The paper presents a novel hydrodynamic approach to solving the dynamic load balancing problem on a network of heterogeneous computers. The computing system consists of a network of processors with different capacities. In the hydrodynamic approach, each processor is viewed as a liquid cylinder where the cross-sectional area corresponds to the capacity of the processor, the communication links are modeled as liquid channels between the cylinders, and the workload is represented as liquid. An algorithm is proposed to simulate the movement of the liquid such that when the algorithm terminates, the heights of the liquid columns are the same in all the cylinders. In this way, each processor obtains an amount of workload proportional to its capacity. This system is analyzed mathematically, and it is proved that the proposed algorithm converges geometrically.

Flexible and extensible load balancing

This paper presents the design philosophy and implementation of the BALANCE system. BALANCE is a flexible, network independent and computer architecture independent load balancing system which allows the building of reusable parallel and distributed applications. By implementing related services as bi generic servers with their connection endpoints registered in BALANCE, the clients can easily access the servers by server system calls. To demonstrate the flexibility of BALANCE, several widely different applications have been implemented and evaluated, including system servers, parallel and distributed applications and a scheduling testbed. The use of generic servers to improve system modularity and code reuse is also discussed.

Multidomain load balancing

This paper investigates dynamic load balancing issues in the multidomain environment where local area networks (LANs) are interconnected by the Internet. Because of the much slower Internet communication speed and limited bandwidth, existing load balancing algorithms for LANs are unsuitable for the multidomain environment. New issues such as lag time in updating load information and network cost of transferring jobs must be addressed. To tackle these problems, the conventional least load scheduler is extended to the multidomain environment by employing a hierarchical structure, and several quick update techniques are proposed. Also, a heuristic taking both the machine load and the network cost into consideration is developed to evaluate the benefits of sending jobs to computers in different domains. A set of experiments conducted on the BALANCE testbed showed that the proposed techniques provide significant performance improvement over existing algorithms.

Efficient load balancing in interconnected LANs using group communication

The paper investigates the use of group communication to improve the efficiency of load balancing in interconnected LANs. Conventional load balancing techniques usually assume point-to-point connections among the computers and typically work on a single LAN only. This may waste network bandwidth and lengthen the load balancing time in LANs that support group communication such as the Ethernet. To tackle this problem a two level algorithm is proposed. At the LAN level, all computers in a LAN maintain loading information in the entire LAN using a globally ordered group channel. The workload in the different LANs is balanced by moving load from the overloaded LANs to the underloaded ones. It is proved that the proposed algorithm converges to the state of global balance geometrically. Experimental results show that the algorithm reduces load balancing time and network utilization significantly, compared to the single level algorithm without group communication.

BALANCE-a flexible parallel load balancing system for heterogeneous computing systems and networks

The design philosophy and implementation of the BALANCE system is described. BALANCE is a flexible, network independent and computer architecture independent load balancing system which is designed to support a wide range of software, including parallel and distributed applications as well as schedulers. The generic server and server system call structures are used as bases to enhance flexibility and to build complex services. BALANCE is not tied to a particular scheduling algorithm, rather the users are allowed to build their own schedulers. To demonstrate the flexibility and power of BALANCE, a set of system services and scheduling algorithms has been implemented and evaluated. A new delay scheduling algorithm which postpones the execution of jobs in high load situation is proposed. It is shown that this algorithm effectively improves system throughput and yet bounds the response times for the console commands.

Minimal communication cost software construction in the Internet environment

Abstract. This paper investigates the issue of building software in the Internet environment, where local area network (LAN) based systems are interconnected by links with different bandwidth and do not share file systems. The software is modeled as a directed acyclic graph. Each node in the graph represents a logical step in processing the software while the edges describe the order of execution. The problem is to construct the software at a particular LAN with minimum Internet communication cost. An optimal polynomial algorithm, SOFTCON, with time complexity