Le 22/02/2023 à 07:01, Kautuk Consul a écrit :
> 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 <kcon...@linux.vnet.ibm.com>
> ---
> 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
This line shouldn't be changed by your patch
> +#undef rmb
> +#undef wmb
I see no point with defining something and undefining them a few lines
later.
Instead, why not do:
#define mb() __asm__ __volatile__ ("sync" : : : "memory")
#if defined(CONFIG_PPC64) || defined(CONFIG_PPC_E500MC)
#define rmb() ({__asm__ __volatile__ ("lwsync" : : : "memory"); })
#define wmb() ({__asm__ __volatile__ ("lwsync" : : : "memory"); })
#else
#define rmb() __asm__ __volatile__ ("sync" : : : "memory")
#define wmb() __asm__ __volatile__ ("sync" : : : "memory")
#endif
By the way, why put it inside a ({ }) ?
And I think nowdays we use "asm volatile" not "__asm__ __volatile__"
Shouldn't you also consider the same for mb() ?
Note that your series will conflict with b6e259297a6b ("powerpc/kcsan:
Memory barriers semantics") in powerpc/next tree.
> +/* Redefine rmb() to lwsync. */
WHat's the added value of this comment ? Isn't it obvious in the line
below that rmb() is being defined to lwsync ? Please avoid useless comments.
> +#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
This line shouldn't be changed by your patch
> +#define SMPWMB mbar
> #else
> -# define SMPWMB eieio
This line shouldn't be changed by your patch
> +#define SMPWMB eieio
> #endif
>
> /* clang defines this macro for a builtin, which will not work with runtime
> patching */
