To reduce inter-CPU bus traffic, code trying to acquire a lock should loop reading without trying to write anything until it reads a changed value. Because of MESI caching protocols, this causes the cache line for the lock to become "Shared"; then there is remarkably "no" bus traffic while a CPU waits for the lock. This optimization is effective on all CPU architectures that have a cache per CPU, because MESI is so widespread. On Hyper-Threading CPUs, pausing with codice_1 gives additional performance by hinting the core that it can work on the other thread while the lock spins waiting.