GridX1 is a computational grid deployment of off-theshelf components using shared resources at several Canadian research institutions. This work evaluates the applicability of knapsack-based resource scheduling to real grids, such as GridX1, by simulating the execution of a real job trace (the NPACI JOBLOG). The task interarrival time is scaled to demonstrate the benefits of the knapsack strategy when operating under heavy workloads. Measurements are made of the effect of varying the task reallocation period \tau and the task value scaling factor \alpha. The knapsack-based allocation strategies are shown to result in allocations which are consistent with the defined policies.