On Sunday 09 September 2007 19:18, Arjan van de Ven wrote:

On Sun, 9 Sep 2007 19:02:54 +0100
Denys Vlasenko [off-list ref] wrote:

quoted

Why is all this fixation on "volatile"? I don't think
people want "volatile" keyword per se, they want atomic_read(&x) to
_always_ compile into an memory-accessing instruction, not register
access.

and ... why is that?
is there any valid, non-buggy code sequence that makes that a
reasonable requirement?

Well, if you insist on having it again:

Waiting for atomic value to be zero:

        while (atomic_read(&x))
                continue;

gcc may happily convert it into:

        reg = atomic_read(&x);
        while (reg)
                continue;

Expecting every driver writer to remember that atomic_read is not in fact
a "read from memory" is naive. That won't happen. Face it, majority of
driver authors are a bit less talented than Ingo Molnar or Arjan van de Ven ;)
The name of the macro is saying that it's a read.
We are confusing users here.

It's doubly confusing that cpy_relax(), which says _nothing_ about barriers
in its name, is actually a barrier you need to insert here.
--
vda