On Thu, Nov 02, 2017 at 04:21:56PM -0400, Alan Stern wrote: > I was trying to think of something completely different. If you have a > release/acquire to the same address, it creates a happens-before > ordering: > > Access x > Release a > Acquire a > Access y > > Here is the access to x happens-before the access to y. This is true > even on x86, even in the presence of forwarding -- the CPU still has to > execute the instructions in order. But if the release and acquire are > to different addresses: > > Access x > Release a > Acquire b > Access y > > then there is no happens-before ordering for x and y -- the CPU can > execute the last two instructions before the first two. x86 and > PowerPC won't do this, but I believe ARMv8 can. (Please correct me if > it can't.)
Release/Acquire are RCsc on ARMv8, so they are ordered irrespective of address. Will
