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

?

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