On Wed, Feb 22, 2023 at 02:33:44PM +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.
>
> Signed-off-by: Kautuk Consul <kcon...@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/barrier.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/barrier.h
> b/arch/powerpc/include/asm/barrier.h
> index b95b666f0374..e088dacc0ee8 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -36,8 +36,15 @@
> * heavy-weight sync, so smp_wmb() can be a lighter-weight eieio.
> */
> #define __mb() __asm__ __volatile__ ("sync" : : : "memory")
> +
> +/* The sub-arch has lwsync. */
> +#if defined(CONFIG_PPC64) || defined(CONFIG_PPC_E500MC)
> +#define __rmb() __asm__ __volatile__ ("lwsync" : : : "memory")
> +#define __wmb() __asm__ __volatile__ ("lwsync" : : : "memory")
Hmmm...
Does the lwsync instruction now order both cached and uncached accesses?
Or have there been changes so that smp_rmb() and smp_wmb() get this
definition, while rmb() and wmb() still get the sync instruction?
(Not seeing this, but I could easily be missing something.)
Thanx, Paul
> +#else
> #define __rmb() __asm__ __volatile__ ("sync" : : : "memory")
> #define __wmb() __asm__ __volatile__ ("sync" : : : "memory")
> +#endif
>
> /* The sub-arch has lwsync */
> #if defined(CONFIG_PPC64) || defined(CONFIG_PPC_E500MC)
> --
> 2.31.1
>
