Re: [lttng-dev] [PATCH 04/11] urcu/arch/generic: Use atomic builtins if configured

["Paul E. McKenney via lttng-dev" <lttng-dev@lists.lttng.org>]

On Mon, May 15, 2023 at 04:17:11PM -0400, Olivier Dion wrote:
> If configured to use atomic builtins, implement SMP memory barriers in
> term of atomic builtins if the architecture does not implement its own
> version.
> 
> Change-Id: Iddc4283606e0fce572e104d2d3f03b5c0d9926fb
> Co-authored-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: Olivier Dion <odion@efficios.com>
> ---
>  include/urcu/arch/generic.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/urcu/arch/generic.h b/include/urcu/arch/generic.h
> index be6e41e..e292c70 100644
> --- a/include/urcu/arch/generic.h
> +++ b/include/urcu/arch/generic.h
> @@ -43,6 +43,14 @@ extern "C" {
>   * GCC builtins) as well as cmm_rmb and cmm_wmb (defaulting to cmm_mb).
>   */
>  
> +#ifdef CONFIG_RCU_USE_ATOMIC_BUILTINS
> +
> +# ifndef cmm_smp_mb
> +#  define cmm_smp_mb() __atomic_thread_fence(__ATOMIC_SEQ_CST)
> +# endif
> +
> +#endif	/* CONFIG_RCU_USE_ATOMIC_BUILTINS */
> +
>  #ifndef cmm_mb
>  #define cmm_mb()    __sync_synchronize()

Just out of curiosity, why not also implement cmm_mb() in terms of
__atomic_thread_fence(__ATOMIC_SEQ_CST)?  (Or is that a later patch?)

							Thanx, Paul

>  #endif
> -- 
> 2.39.2
> 
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