A Decentralized and Efficient Algorithm for Load Sharing in Networks of Workstations

This paper presents the design and evaluation of a decentralized load sharing algorithm for networks of workstations, RADIO. With respect to general distributed computing environments, networks of workstations have some peculiarities. First, the global computing power is most of the time much underutilized. Second, users of workstations need occasionally a peek of computing power. Third, workstations are often diskless, so that running a process on one workstation or another does not add file migration overhead. Fourth, network interfaces often provide a broadcast capability, which may be used to reach several destinations in a single message. Last, workstations are often dedicated to an "owner", so that a workstation may only be used for running foreign processes only when the workstation’s owner does not use it (or at least when running foreign processes would not increase the owner’s programs response time by a significant amount). The first three points make load sharing very attractive for a network of workstations. The fourth point may be used for simplifying the design of load sharing algorithms, but broadcasting is expensive. The goal of RADIO is to provide the benefits of a decentralized load sharing algorithm while preserving the personal character of workstations and providing good performance results, in particular with respect to extensibility. The key feature of the RADIO load sharing algorithm is that it is decentralized but involves expensive broadcast messages only occasionally. The design choices for information policy, location policy and transfer policy are described and motivated. RADIO has been implemented on a network of Sun workstations, and runs entirely outside of the kernel. Experimental results show that the extensibility of RADIO is better than that of previous decentralized algorithms, based on broadcast messages.