Re: [lttng-dev] [PATCH v2 04/12] urcu/system: Use atomic builtins if configured

On Wed, Jun 07, 2023 at 02:53:51PM -0400, Olivier Dion wrote:
> If configured to use atomic builtins, use them for implementing the
> CMM_LOAD_SHARED and CMM_STORE_SHARED macros.
> 
> Change-Id: I3eaaaaf0d26c47aced6e94b40fd59c7b8baa6272
> Co-authored-by: Mathieu Desnoyers <[email protected]>
> Signed-off-by: Olivier Dion <[email protected]>
> ---
>  include/urcu/system.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/urcu/system.h b/include/urcu/system.h
> index faae390..f184aad 100644
> --- a/include/urcu/system.h
> +++ b/include/urcu/system.h
> @@ -19,9 +19,28 @@
>   * all copies or substantial portions of the Software.
>   */
>  
> +#include <urcu/config.h>
>  #include <urcu/compiler.h>
>  #include <urcu/arch.h>
>  
> +#ifdef CONFIG_RCU_USE_ATOMIC_BUILTINS
> +
> +#define CMM_LOAD_SHARED(x)			\
> +	__atomic_load_n(&(x), __ATOMIC_RELAXED)
> +
> +#define _CMM_LOAD_SHARED(x) CMM_LOAD_SHARED(x)
> +
> +#define CMM_STORE_SHARED(x, v)					\
> +	__extension__						\
> +	({							\
> +		__typeof__(v) _v = (v);				\
> +		__atomic_store_n(&(x), _v, __ATOMIC_RELAXED);	\
> +		_v;						\
> +	})
> +
> +#define _CMM_STORE_SHARED(x, v) CMM_STORE_SHARED(x, v)

Same question here on loss of volatile semantics.

							Thanx, Paul

> +
> +#else
>  /*
>   * Identify a shared load. A cmm_smp_rmc() or cmm_smp_mc() should come
>   * before the load.
> @@ -56,4 +75,6 @@
>  		_v = _v;	/* Work around clang "unused result" */	\
>  	})
>  
> +#endif	/* CONFIG_RCU_USE_ATOMIC_BUILTINS */
> +
>  #endif /* _URCU_SYSTEM_H */
> -- 
> 2.40.1
> 
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