Yes because of the "it's the cold of path" aspect. That said, CAS is often considerably slower than an atomic increment replacement even if the usual sources re

Yes because of the "it's the cold of path" aspect. That said, CAS is often considerably slower than an atomic increment replacement even if the usual sources report equal throughout because the dependency chains to both the output value and flags (i.e., the "succeeded?" indicator) usually involves a load of the value, and an operation to manipulate it prior to using it in the CAS. So even if a CAS never fails it can end up half a dozen cycles slower if this chain matters (and it often does). That aspect fails to be captured by say uops.info which just tries to isolate the effect of the instruction alone. Of, course, the even more important reason to use unconditional ops on a contended path if you can is that they don't fail: CAS retries will be significant in that case (but this doesn't apply here because "one off cold path").