Improving The Performance Of PVM Using Multicast Technology

With the development of network technology and the appearance of highly efficient work station, people demand more from resources sharing. Through network, users can share and exchange information within a large scope. If only connecting computers with network without providing software support, the network cannot be counted as highly efficient parallel computer system and has no essential difference from common computer local area network. Therefore, parallel program design environment's research is a very active research field and wins attention at home and abroad. And the network of workstation is a direction of new technology in parallel processing area and an effective way in realizing highly efficient computer system. PVM system is an all-purpose parallel program design system, providing the message passing, process creation and synchronization editing parallel program needs. While in realizing message passing, PVM system adopts point-to-point communications technology to realize group communications in order to realize transplantation. Such an adoption not only wastes the bandwidth but also proves inefficient. At present, an efficient way of utilizing present bandwidth is multicast technology which is a one-to-many communications technology, that is, a way to receive same messages from one source to many receivers. It can improve communications efficiency by perfecting PVM system, reduce the bandwidth the group communications occupy and decrease the burden of the host computer and network.This paper introduces the message mechanism of PVM, elaborates the rationale of the parallel program based upon the development method of PVM and basic computer model. By analyzing the communications characteristics of distributed computing system( in parallel programs operation exists large quantity of group communications) it is concluded that improving highly efficient group communications mechanism can perfect the distributed computing system and that improving PVM system can perfect the efficiency of the parallel program operation. It is quite necessary to improve the group communications of PVM system.In order to improve the communications efficiency, reduce the bandwidth the group communications occupy and decrease the burden of the host computer and the network, two ways are available in dealing with this. One is to adopt a network more efficient such as highly efficient parallel HiPPI and Myrinet; the other is to reduce the number of message transmitted in communications network, according to the characteristics of communications in distributed computing system. In many cases, the former is not a feasible method, for users mostly hope to gain highly efficient counting in present conditions of network. The reason for using the distributed computing system is its cheapness while the adoption of more efficient computer network or specially designed network undoubtedly increase the cost. Therefore, developing highly efficient communications technology is a must to improve communications efficiency.Group communications of PVM is realized by Unicast. The host computer responsible for sending message must send a single data package copy to every receiver and this will burden the source host computer, for it must give responses to every demand, thus prolonging the time, reducing the effectiveness and occupying too big percentage of the bandwidth in multi-sending group communications. Being aware of the weak points of unicast, the notion of multicast is put forward. Group communications are effective in parallel and distributed system. This paper is to utilize the Multicast to realize PVM group communications, i.e. the one to many communications.After describing group communications' scheme, the PVM group communications are discussed in detail. A host computer can send message to a multicast group. Any computers interested in this can receive such message. The improved PVM task group address can correspond to a multicast address. The entire message sent to this task group can multicast to the correspondent m...