Re: [PATCH 1/5] atomics: add acquire/release/relaxed variants of some atomic operations

Peter Zijlstra
2015-07-14T11:24:27Z

On Tue, Jul 14, 2015 at 12:08:11PM +0100, Will Deacon wrote:
> On Tue, Jul 14, 2015 at 11:58:37AM +0100, Peter Zijlstra wrote:

> > #ifndef atomic_add_return_relaxed
> >
> > #define atomic_add_return_relaxed atomic_add_return
> > /*
> > * If one cannot define a more relaxed version,
> > * acquire/release are out the window too.
> > */
> > #define atomic_add_return_acquire atomic_add_return
> > #define atomic_add_return_release atomic_add_return
> >
> > #else /* relaxed */
> >
> > #ifndef atomic_add_return_acquire
> > #define atomic_add_return_acquire(args...) \
> > do { \
> > atomic_add_return_relaxed(args); \
> > smp_mb__after_atomic(); \
> > } while (0)
> > #endif
> >
> > #ifndef atomic_add_return_release
> > #define atomic_add_return_release(args...) \
> > do { \
> > smp_mb__before_atomic(); \
> > atomic_add_return_relaxed(args); \
> > } while (0)
> > #endif

One could even take it one step further and go:

#ifndef atomic_add_return
#define atomic_add_return(args...) \
do { \
smp_mb__before_atomic(); \
atomid_add_return_relaxed(args); \
smp_mb__after_atomic(); \
} while (0)

> >
> > #endif /* relaxed */
>
> If a picture is worth a thousand words, a patch is worth at least a thousand
> pictures.

:-)