Idletime Scheduling with Preemption Intervals

摘要

This paper presents the idletime scheduler; a generic, kernel-level mechanism for using idle resource capacity in the background without slowing down concurrent foreground use. Many operating systems fail to support transparent background use and concurrent foreground performance can decrease by 50% or more. The idletime scheduler minimizes this interference by partially relaxing the work conservation principle during preemption intervals, during which it serves no background requests even if the resource is idle. The length of preemption intervals is a controlling parameter of the scheduler: short intervals aggressively utilize idle capacity; long intervals reduce the impact of background use on foreground performance. Unlike existing approaches to establish prioritized resource use, idletime scheduling requires only localized modifications to a limited number of system schedulers. In experiments, a FreeBSD implementation for idletime network scheduling maintains over 90% of foreground TCP throughput, while allowing concurrent, high-rate UDP background flows to consume up to 80% of remaining link capacity. A FreeBSD disk scheduler implementation maintains 80% of foreground read performance, while enabling concurrent background operations to reach 70% throughput.