svn commit: r358733 - head/sys/sys

[Andriy Gapon]

On 12/03/2020 09:48, Alan Cox wrote:
> Just to be clear, this is not just a matter of whether our release fences are
> poorly or inefficiently implemented.  Release fences (as defined by the C/C++
> standards that inspire our atomics) have *different* semantics than release
> stores. Specifically, a release fence places more ordering restrictions on the
> nearby store accesses than a release store does.  (In fact, "man 9 atomic"
> describes this.)  Thus, it is almost inevitable that a release fence will have a
> higher cost than the best possible implementation of a release store.

For people like me who are new to these things here is a good explanation
(perhaps a bad title, though):
https://preshing.com/20131125/acquire-and-release-fences-dont-work-the-way-youd-expect/

-- 
Andriy Gapon