Re: [PATCH v2 01/12] locking/atomic: Introduce inc/dec calls for FETCH-OP flavors

[Peter Zijlstra]

On Fri, Jun 24, 2016 at 09:34:30AM -0700, Davidlohr Bueso wrote:
> On Thu, 23 Jun 2016, Peter Zijlstra wrote:
> 
> >-
> >/* atomic_fetch_inc_relaxed */
> >#ifndef atomic_fetch_inc_relaxed
> >+
> >+#ifndef atomic_fetch_inc
> 
> #define atomic_fetch_inc(v)  (atomic_fetch_add(1, v))

Ah yes.

> >+#define atomic_fetch_inc_relaxed(v)	atomic_fetch_add_relaxed(1, (v))
> >+#define atomic_fetch_inc_acquire(v)	atomic_fetch_add_acquire(1, (v))
> >+#define atomic_fetch_inc_release(v)	atomic_fetch_add_release(1, (v))
> 
> I was under the impression that if the archs don't define their own calls,
> then we always default to fully ordered. Which is why I based all this ifdefery
> on what is currently done with the other atomic_fetch_$ops.

Right, but this allows an arch to only define atomic_fetch_add_relaxed()
and have the various forms of fetch_inc() instantiated as well.

With your earlier version they would all fall back to the fully
sequential variant of fetch_add().