Efficiently Scheduling Advance Reservations in Grids Umar Farooq, Shikharesh Majumdar, Eric W. Parsons Department of Systems and Computer Engineering Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6 {ufarooq, majumdar}@ sce.carleton.ca, eparsons@acm.org Carleton University Department of Systems and Computer Engineering Technical Report SCE-05-14, August 2005. © 2005 Umar Farooq, Shikharesh Majumdar and Eric W. Parsons Abstract Advance reservations (ARs) were introduced for application-level dynamic scheduling of resources in a Grid infrastructure. Advance reservations of resources for a specific time in future not only ensure that all resources would be simultaneously available at the execution time of the application but also ensure that the QoS constraints of the Grid applications would be met. Previous research shows that ARs can meet their objectives but at a significant performance cost. In this paper, we argue that laxity in the reservation window of an AR can help improve performance of scheduling with advance reservations. Scheduling ARs with given laxities is an NP-Hard problem and the paper presents a scalable algorithm for scheduling on-demand and advance reservation requests with laxities. The paper then investigates in detail the effect of proportion of advance reservations, laxity and distribution of the size of tasks on performance through extensive experimentation. The paper also investigates that how much improvement in performance can be gained by task preemption and up to what percentage of overheads is preemption justified in scheduling of on-demand and advance reservation requests. We demonstrate how, for some workloads, laxity can be exchanged for preemption to achieve high utilization. Finally, the paper studies resource level policies to prevent starvation of on-demand requests. Key Words: Computational/Data Grids, Resource Management in Grids, Advance Reservations, Grid Scheduler, Grid System Performance, Scheduling with Deadlines.