Wan-Oh Yoon

Task scheduling algorithm using minimized duplications in homogeneous systems

For fine grain task graphs, duplication-based scheduling algorithms are generally more efficient than list and cluster-based algorithms. However, most duplication-based heuristics try to duplicate all possible ancestor nodes of a given join node, in order to reduce the earliest start time (EST) of the join node, even though these ancestor nodes have already been allocated in previous steps. Thus, these duplication heuristics inevitably induce redundant duplications, which lead to the superfluous consumption of resources and generally deteriorate the scheduling result in the case of a bounded number of processors. When scheduling algorithms are used on an unbounded number of processors, the required number of processors grows excessively with the size of the task graph, thereby limiting the practicality of these algorithms for large task graphs. In this paper, we propose a novel algorithm designed to allocate join nodes without redundant duplications. In the proposed algorithm, if the ancestor nodes of a join node are duplicated when scheduling the join node, the original allocations of these ancestor nodes are removed using a very efficient method. The performance of the proposed algorithm, in terms of its normalized schedule length and efficiency, is compared with that of some of the recently proposed algorithms. The proposed algorithm generates better or comparable schedules with minimized duplication. Specifically, the simulation results show that it is most useful on a bounded number of processors.

Task Scheduling Algorithm with Minimal Redundant Duplications in Homogeneous Multiprocessor System

The performance of a homogeneous multiprocessor system depends on an algorithm which schedules input DAG. Among various task scheduling algorithms, ones that are using full duplication provide superior performance by duplicating tasks recursively. However, redundant duplications lead to increase of total execution time and decrease of processor idle time. In this paper, we propose GDRA which reduces total execution time and increases processor idle time by eliminating redundant duplications. Comparisons with other full duplication algorithms, such as CPFD, SD, and MDJ, show that GDRA provides the better performance as the CCR increases.

MPEG-4 stream transmission and synchronization for parallel servers

Our new multimedia transmission and synchronization scheme for parallel servers in a wireless environment enables servers to store MPEG-4 data according to video-object-plane type. The goal of our research, therefore, was to develop an enhanced multimedia transmission scheme that can cope with load imbalance, congestion, and jitter. Accordingly, we evaluated three issues: data striping, priority queuing, and multimedia synchronization.

VOD multicast using CIWP and p2p partial stream transfer

Providing VOD in the internet is one of the challenging technologies. When a new client joins an ongoing multicast session for VOD service, the servers using CIWP scheme for the VOD multicast creates an additional unicast channel to serve the partial stream. And, the unicast channel consumes a certain amount of the I/O bandwidth of the server, as well as some of the network resources between the server and clients. This problem can be solved by using p2p local transfer between the clients to deliver the partial stream. In this paper, we propose a new VOD multicast scheme that is based on the CIWP scheme and the p2p transfer of the partial multimedia stream. In the p2p approach, unexpected dropout of a client, due to the failure of the connection or departure from the current session, can disrupt the partial stream transfer for the other clients. Thus, we also propose a procedure to recover from this kind of unexpected dropout. Our simulation results show that the proposed scheme reduces the network bandwidth on the server side dramatically, reduces the average waiting time of the client, and improves the service quality.