Re: [PATCH] arch/powerpc/include/asm/barrier.h: redefine rmb and wmb to lwsync

From: Kautuk Consul
Date: Wed Feb 22 2023 - 04:08:41 EST


Sorry, sent the wrong patch!
Please ignore this one.
Sending the v2 in another email.

On Wed, Feb 22, 2023 at 02:31:12PM +0530, Kautuk Consul wrote:
> A link from ibm.com states:
> "Ensures that all instructions preceding the call to __lwsync
> complete before any subsequent store instructions can be executed
> on the processor that executed the function. Also, it ensures that
> all load instructions preceding the call to __lwsync complete before
> any subsequent load instructions can be executed on the processor
> that executed the function. This allows you to synchronize between
> multiple processors with minimal performance impact, as __lwsync
> does not wait for confirmation from each processor."
>
> Thats why smp_rmb() and smp_wmb() are defined to lwsync.
> But this same understanding applies to parallel pipeline
> execution on each PowerPC processor.
> So, use the lwsync instruction for rmb() and wmb() on the PPC
> architectures that support it.
>
> Also removed some useless spaces.
>
> Signed-off-by: Kautuk Consul <kconsul@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/barrier.h | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> index e80b2c0e9315..553f5a5d20bd 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -41,11 +41,17 @@
>
> /* The sub-arch has lwsync */
> #if defined(CONFIG_PPC64) || defined(CONFIG_PPC_E500MC)
> -# define SMPWMB LWSYNC
> +#undef rmb
> +#undef wmb
> +/* Redefine rmb() to lwsync. */
> +#define rmb() ({__asm__ __volatile__ ("lwsync" : : : "memory"); })
> +/* Redefine wmb() to lwsync. */
> +#define wmb() ({__asm__ __volatile__ ("lwsync" : : : "memory"); })
> +#define SMPWMB LWSYNC
> #elif defined(CONFIG_BOOKE)
> -# define SMPWMB mbar
> +#define SMPWMB mbar
> #else
> -# define SMPWMB eieio
> +#define SMPWMB eieio
> #endif
>
> /* clang defines this macro for a builtin, which will not work with runtime patching */
> --
> 2.31.1
>