Yes, CPU would have to make sure that only one thread is updating the value and this would definitely increase latency for other threads.
"Guaranteed forward progress" is barely of any interest here. They actually mean, that in the event of a thread randomly stopping for some reason, other threads will still be able to perform atomic operations, because no thread can actually stop in the middle of an atomic operation.
"Guaranteed forward progress" is barely of any interest here. They actually mean, that in the event of a thread randomly stopping for some reason, other threads will still be able to perform atomic operations, because no thread can actually stop in the middle of an atomic operation.