In this paper we evaluate the performance implications of using a buddy scheme for contiguous node allocation, in conjunction with a backfilling job scheduler for clusters. When a contiguous node allocation strategy is used, there is a trade-off between improved run-time of jobs (due to reduced link contention and lower communication overhead) and increased wait-time of jobs (due to external fragmentation of the processor system). Using trace-based simulation, a buddy strategy for contiguous node allocation is shown to be unattractive compared to the standard noncontiguous allocation strategy used in all production job schedulers. A simple but effective scheme for selective buddy allocation is then proposed, that is shown to perform better than non-contiguous allocation.

Even though middleware support for grid computing has been the subject of extensive research, scheduling policies for the grid context have not been much studied. In addition to processor utilization, it is important to consider the response times of jobs in evaluating the performance of grid scheduling strategies. In this paper we propose distributed scheduling algorithms that use multiple simultaneous requests at different sites. Trace-based simulations show that the use of multiple simultaneous requests provides significant performance benefits. We also show how this scheme can be adapted to provide priority to local jobs, without much loss of performance.

Although theoretical results have been established regarding the utility of pre-emptive scheduling in reducing average job turn-around time, job suspension/restart is not much used in practice at supercomputer centers for parallel job scheduling. A number of questions remain unanswered regarding the practical utility of pre-emptive scheduling. We explore this issue through a simulation-based study, using job logs from a supercomputer center We develop a tunable selective-suspension strategy, and demonstrate its effectiveness. We also present new insights into the effect of pre-emptive scheduling on different job classes and address the impact of suspensions on worst-case slowdown.