On Thu, Mar 10, 2022 at 09:05:54AM +0000, Visa Hankala wrote: > > As a bonus alpha gets the membar it needs. > > In general, atomic_* functions have not provided implicit memory > barriers on OpenBSD. > > I am not sure if the data dependency barrier is needed where > atomic_load_int() and atomic_load_long() are used. The memory ordering > guarantee is very weak and does not seem useful in any of the use cases > in the patch. However, the barrier does not appear to make things worse > in terms of correctness. Except maybe in assertions where they cause > subtle side effects.
Our atomic functions don't provide barriers. The only exception is reading on Alpha. The idea of membar_datadep_consumer() is taken from Linux arch/alpha/include/asm/rwonce.h. As I understand it, Alpha CPU may have more than one data cache. So you need a barrier between reading a pointer and using its value. Without knowing the details, we just do what Linux does. bluhm
