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SubjectRe: [PATCH v2 15/32] powerpc: define __smp_xxx
Hi Michael,

On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:
> This defines __smp_xxx barriers for powerpc
> for use by virtualization.
>
> smp_xxx barriers are removed as they are
> defined correctly by asm-generic/barriers.h
>
> This reduces the amount of arch-specific boiler-plate code.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> ---
> arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
> 1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> index 980ad0c..c0deafc 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -44,19 +44,11 @@
> #define dma_rmb() __lwsync()
> #define dma_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
>
> -#ifdef CONFIG_SMP
> -#define smp_lwsync() __lwsync()
> +#define __smp_lwsync() __lwsync()
>

so __smp_lwsync() is always mapped to lwsync, right?

> -#define smp_mb() mb()
> -#define smp_rmb() __lwsync()
> -#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> -#else
> -#define smp_lwsync() barrier()
> -
> -#define smp_mb() barrier()
> -#define smp_rmb() barrier()
> -#define smp_wmb() barrier()
> -#endif /* CONFIG_SMP */
> +#define __smp_mb() mb()
> +#define __smp_rmb() __lwsync()
> +#define __smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
>
> /*
> * This is a barrier which prevents following instructions from being
> @@ -67,18 +59,18 @@
> #define data_barrier(x) \
> asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
>
> -#define smp_store_release(p, v) \
> +#define __smp_store_release(p, v) \
> do { \
> compiletime_assert_atomic_type(*p); \
> - smp_lwsync(); \
> + __smp_lwsync(); \

, therefore this will emit an lwsync no matter SMP or UP.

Another thing is that smp_lwsync() may have a third user(other than
smp_load_acquire() and smp_store_release()):

http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877

I'm OK to change my patch accordingly, but do we really want
smp_lwsync() get involved in this cleanup? If I understand you
correctly, this cleanup focuses on external API like smp_{r,w,}mb(),
while smp_lwsync() is internal to PPC.

Regards,
Boqun

> WRITE_ONCE(*p, v); \
> } while (0)
>
> -#define smp_load_acquire(p) \
> +#define __smp_load_acquire(p) \
> ({ \
> typeof(*p) ___p1 = READ_ONCE(*p); \
> compiletime_assert_atomic_type(*p); \
> - smp_lwsync(); \
> + __smp_lwsync(); \
> ___p1; \
> })
>
> --
> MST
>
> --
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