Hierarchical Backoff Locks for Nonuniform Communication Architectures

This paper identifies node affinity as an important property for scalable general-purpose locks. Nonuniform communication architectures (NUCAs), for example CCNUMAs built from a few large nodes or from chip multiprocessors (CMPs), have a lower penalty for reading data from a neighbor’s cache than from a remote cache. Lock implementations that encourages handing over locks to neighbors will improve the lock handover time, as well as the access to the critical data guarded by the lock, but will also be vulnerable to starvation. We propose a set of simple software-based hierarchical backoff locks (HBO) that create node affinity in NUCAs. A solution for lowering the risk of starvation is also suggested. The HBO locks are compared with other softwarebased lock implementations using simple benchmarks, and are shown to be very competitive for uncontested locks while being more than twice as fast for contended locks. An application study also demonstrates superior performance for applications with high lock contention and competitive performance for other programs.