Gang Scheduling with a Queue for Large Jobs

Applying gang scheduling can alleviate the blockade problem caused by exclusively space-sharing scheduling. To simply allow jobs to run simultaneously on the same processors as in conventional gang scheduling, however, may introduce a large number of time slots in the system. In consequence the cost of context switches will be greatly increased, and each running job can only obtain a small portion of resources including memory space and processor utilisation and so no jobs can nish their computations quickly. Therefore, the number of jobs allowed to run in the system should be limited. In this paper we present some experimental results to show that by limiting real large jobs timesharing the same processors and applying the back lling technique we can greatly reduce the average number of time slots in the system and signi cantly improve the performance of both small and large jobs.