Messages in this thread | | | From | Christophe Leroy <> | Subject | Re: [PATCH] arch/powerpc/include/asm/barrier.h: redefine rmb and wmb to lwsync | Date | Wed, 22 Feb 2023 07:02:34 +0000 |
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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 <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
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 */
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