On Sunday 09 September 2007 19:18, Arjan van de Ven wrote:
> On Sun, 9 Sep 2007 19:02:54 +0100
> Denys Vlasenko <[email protected]> wrote:
>
> > 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
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