When is RCU the right choice over spinlocks or mutexes?
RCU shines in read-heavy workloads with frequent updates to small parts of state: routing tables, config hotpaths, ACL lists. If reads vastly outnumber writes and readers spend little time in critical sections, RCU's zero-contention reads dominate. It costs extra complexity for writes and synchronization.
Answered in
How Linux RCU Unlocks Read-Side ScalingRCU lets millions of readers run lock-free while a single writer updates state by copying, mutating off-to-the-side, and atomically flipping a pointer.
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