The effect of deceptive idleness on disk schedulers

Disk schedulers in operating systems are generally work-conserving; they schedule a request immediately after the previous request has finished. Such schedulers need mul-tiple outstanding requests to make good decisions. Unfortunately, many applications issue synchronous, almost-continuous streams of read requests. This forces the sched-uler into making decisions too early, falsely assuming that the process has become momentarily idle. This phenomenon of deceptive idleness causes significant degrada-tion in performance and quality of service objectives on current systems. We solve deceptive idleness by designing and implementing a transparent, non-work-conserving scheduling framework for various scheduling policies. We evaluate this solution on mi-crobenchmarks and real workloads, and observe large benefits. The Apache webserver delivers 56 % and 16 % more throughput for two configurations. The Andrew Bench-mark runs faster by 8 % (54 % for the read-intensive phase). Variants of the TPC-B database benchmark exhibit improvements between 4 % and 60%. Proportional-share schedulers become empowered to efficiently deliver application-desired proportions