Re: [PATCH 2/7] atomics/treewide: rework ordering barriers

[Peter Zijlstra]

On Tue, Jun 05, 2018 at 02:28:02PM +0100, Mark Rutland wrote:
> On Tue, Jun 05, 2018 at 02:16:23PM +0200, Peter Zijlstra wrote:
> > and simply using smp_mb__{before,after}_atomic for the full fence, its
> > exactly what they were made for.
> 
> The snag is arch/alpha, whare we have:
> 
> /*
>  * To ensure dependency ordering is preserved for the _relaxed and
>  * _release atomics, an smp_read_barrier_depends() is unconditionally
>  * inserted into the _relaxed variants, which are used to build the
>  * barriered versions. To avoid redundant back-to-back fences, we can
>  * define the _acquire and _fence versions explicitly.
>  */
> #define __atomic_op_acquire(op, args...)        op##_relaxed(args)
> #define __atomic_op_fence                       __atomic_op_release
> 
> ... where alpha's smp_read_barrier_depends() is the same as
> smp_mb_after_atomic().
> 
> Since alpha's non-value-returning atomics do not have the
> smp_read_barrier_depends(), I can't just define an empty
> smp_mb_after_atomic().
> 
> Thoughts?

Bah, of course there had to be a misfit.

Something along these lines then:

 __atomic_acquire_fence
 __atomic_release_fence
 __atomic_mb_before
 __atomic_mb_after

?