Re: why are some atomic_t's not volatile, while most are?

Jerry Jiang
2007-08-08T08:22:20Z

On Wed, 08 Aug 2007 02:47:53 -0400
Chris Snook <csnook@redhat.com> wrote:

> Chris Friesen wrote:
> > Chris Snook wrote:
> >
> >> This is not a problem, since indirect references will cause the CPU to
> >> fetch the data from memory/cache anyway.
> >
> > Isn't Zan's sample code (that shows the problem) already using indirect
> > references?
>
> Yeah, I misinterpreted his conclusion. I thought about this for a
> while, and realized that it's perfectly legal for the compiler to re-use
> a value obtained from atomic_read. All that matters is that the read
> itself was atomic. The use (or non-use) of the volatile keyword is

Sorry, I can't understand it a bit .., Could you do in detail?

-- Jerry

> really more relevant to the other atomic operations. If you want to
> guarantee a re-read from memory, use barrier(). This, incidentally,
> uses volatile under the hood.
>
> -- Chris