Re: [RFC PATCH] x86: Use volatile semantics for atomic_set()

From: Peter Zijlstra
Date: Tue Sep 23 2014 - 04:13:06 EST

On Mon, Sep 22, 2014 at 05:42:16PM -0400, Pranith Kumar wrote:
> On Mon, Sep 22, 2014 at 4:08 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Mon, Sep 22, 2014 at 03:39:21PM -0400, Pranith Kumar wrote:
> >> All the atomic operations have volatile semantics to prevent compiler
> >> reordering. Enforce the same semantics for atomic_set() too.
> >
> > To what point? atomic_set() is typically not what you expect it to
> > anyhow.
> This is the only atomic operation which allows compiler reordering. I
> am not sure why this exception was made. Any ideas as to why we do
> this?

Because it typically doesn't matter. And you should never use
atomic_set() where it does matter.
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