Using Lock Servers to Scale Real-Time Locking Protocols: Chasing Ever-Increasing Core Counts (Artifact)

Abstract

During the past decade, parallelism-related issues have been at the forefront of real-time systems research due to the advent of multicore technologies.  In the coming years, such issues will loom ever larger due to increasing core counts.  Having more cores means a greater potential exists for platform capacity loss when the available parallelism cannot be fully exploited.  In this work, such capacity loss is considered in the context of real-time locking protocols.  In this context, lock nesting becomes a key concern as it can result in transitive blocking chains that force tasks to execute sequentially unnecessarily.  Such chains can be quite long on a larger machine.  Contention-sensitive real-time locking protocols have been proposed as a means of ``breaking'' transitive blocking chains, but such protocols tend to have high overhead due to more complicated lock/unlock logic.  To ease such overhead, the usage of lock servers is considered herein.  In particular, four specific lock-server paradigms are proposed and many nuances concerning their deployment are explored.  Experiments are presented that show that, by executing cache hot, lock servers can enable reductions in lock/unlock overhead of up to 86\%.  Such reductions make contention-sensitive protocols a viable approach in practice. This artifact contains the implementation of two contention-sensitive locking protocol variants implemented with four proposed lock-server paradigms, as well as the experiments with which they were evaluated.