On Fri, 14 Jul 2006, Linus Torvalds wrote:
>
> Now, there is a "reason" we'd want "endflag" to either be volatile, or
> have the "set_wmb()", and that is that the code is incorrect in the first
> place.
Btw, and this may just be me, but I personally don't much like the
"set_wmb()" macro. I think it should be removed.
I don't think we actually use it anywhere, and the thing is, it's not
really useful. It is basically _always_ equivalent to
var = value;
smp_wmb();
except I think some architectures could _in_theory_ make the assignment be
a "store with release consistency". The only architecture where that might
make sense that I can think of is Itanium, and even there the ia64
set_wmb() macro doesn't actually do that.
Yeah, the
endflag = 1;
smp_wmb();
is a bit longer, but is actually easier to understand, I think.
I suspect "set_wmb()" was added just from an incorrect sense of
consistency with "set_mb()" (which I don't particularly like either, but
at least that one makes a difference on a real platform, ie on x86 that
"set_mb()" ends up being implemented as a single "xchg" instruction).
Linus
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