In this paper we first introduce the concepts of utilisation ratio and effective speedup and their relations to the system performance. We then describe a two-level scheduling scheme which can be used to achieve good performance for parallel jobs and good response for interactive sequential jobs and also to balance both parallel and sequential workloads. The two-level scheduling can be implemented by introducing on each processor a registration office. We also introduce a loose gang scheduling scheme. This scheme is scalable and has many advantages over existing explicit and implicit coscheduling schemes for scheduling parallel jobs under a time sharing environment.