Messages in this thread | | | Date | Tue, 14 Jul 2015 12:31:47 +0100 | From | Will Deacon <> | Subject | Re: [PATCH 1/5] atomics: add acquire/release/relaxed variants of some atomic operations |
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On Tue, Jul 14, 2015 at 12:24:20PM +0100, Peter Zijlstra wrote: > 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)
...and
#ifndef atomic_add #define atomic_add(args...) (void)atomic_add_return_relaxed(args);
It would mean a new architecture only has to define a barrier instruction and a handful of relaxed atomics for a bare-minimum atomic.h avoiding spinlocks.
Will
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