Re: [PATCH] documentation: ACQUIRE applies to loads, RELEASE applies to stores
From: Paul E. McKenney
Date: Fri Apr 22 2016 - 13:13:57 EST
On Fri, Apr 22, 2016 at 04:32:22PM +0200, Peter Zijlstra wrote:
> On Fri, Apr 22, 2016 at 11:41:49AM +0100, Will Deacon wrote:
> > For compound atomics performing both a load and a store operation, make
> > it clear that _acquire and _release variants refer only to the load and
> > store portions of compound atomic. For example, xchg_acquire is an xchg
> > operation where the load takes on ACQUIRE semantics.
> > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Queued, thank you both!
> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> > ---
> > Documentation/memory-barriers.txt | 5 +++++
> > 1 file changed, 5 insertions(+)
> > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> > index 3729cbe60e41..05f8011011be 100644
> > --- a/Documentation/memory-barriers.txt
> > +++ b/Documentation/memory-barriers.txt
> > @@ -464,6 +464,11 @@ And a couple of implicit varieties:
> > This means that ACQUIRE acts as a minimal "acquire" operation and
> > RELEASE acts as a minimal "release" operation.
> > +A subset of the atomic operations described in atomic_ops.txt have ACQUIRE
> > +and RELEASE variants in addition to fully-ordered and relaxed (no barrier
> > +semantics) definitions. For compound atomics performing both a load and a
> > +store, ACQUIRE semantics apply only to the load and RELEASE semantics apply
> > +only to the store portion of the operation.
> > Memory barriers are only required where there's a possibility of interaction
> > between two CPUs or between a CPU and a device. If it can be guaranteed that
> > --
> > 2.1.4