[gpderetta]

I would say that acquire/release map very well to x86 (were they are free). Technically x86 is slightly stronger as it doesn't allow IRIW, but seq cst is too expensive to implement by default.

Conversely acq/rel are from somewhat to very expensive to implement on ARM/POWER.

[dragontamer]

Acq/rel are nonsense on x86, worse than a NOP. It compiles down into nothing.

x86 cannot specify a load/store any more relaxed than total-store ordering (which is even "stronger" than acquire/release)

ARM / POWER9 were originally "consume/release". But upon C++11, the agreement was that consume/release was too complicated, and acquire/release model was created instead.

Java was the granddaddy of modern memory models but focused on Seq-Cst (the strongest model: the one that makes "sense" to most programmers). C++ inherited Java's seq-cst, but recognized that low-level programmers wanted something faster: both "fully relaxed" and acq/rel as the two faster ways to load/store.