Investigating Split Locks on x86-64

“Split locks” are atomic operations that access memory across cache line boundaries. Atomic operations let programmers perform several basic operations in sequence without interference from another thread. That makes atomic operations useful for multithreaded code. For instance, an atomic test and set can let a thread acquire a higher level lock. Or, an atomic add can let multiple threads increment a shared counter without using a software-orchestrated lock. Modern CPUs handle atomics with cache...