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    SubjectRe: [PATCH] arch/powerpc/include/asm/barrier.h: redefine rmb and wmb to lwsync
    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@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
    > +#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
    >

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