The read-copy-update mechanism for supporting real-time applications on shared-memory multiprocessor systems with Linux

Read-copy update (RCU) is a synchronization mechanism in the Linux™ kernel that provides significant improvements in multiprocessor scalability by eliminating the writer-delay problem of readers-writer locking. RCU implementations to date, however, have had the side effect of expanding non-preemptible regions of code, thereby degrading real-time response. We present here a variant of RCU that allows preemption of read-side critical sections and thus is better suited for real-time applications. We summarize priority-inversion issues with locking, present an overview of the RCU mechanism, discuss our counter-based adaptation of RCU for real-time use, describe an additional adaptation of RCU that permits general blocking in read-side critical sections, and present performance results. We also discuss an approach for replacing the readers-writer synchronization with RCU in existing implementations.