[PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers
olof at lixom.net
Sat Sep 10 03:23:33 EST 2011
On Tue, Sep 6, 2011 at 11:00 AM, Paul E. McKenney
<paulmck at linux.vnet.ibm.com> wrote:
> The trailing isync/lwsync in PowerPC value-returning atomics needs
> to be a sync in order to provide the required ordering properties.
> The leading lwsync/eieio can remain, as the remainder of the required
> ordering guarantees are provided by the atomic instructions: Any
> reordering will cause the stwcx to fail, which will result in a retry.
Admittedly, my powerpc barrier memory is starting to fade, but isn't
isync sufficient here? It will make sure all instructions before it
have retired, and will restart any speculative/issued instructions
lwsync not being sufficient makes sense since a load can overtake it.
> diff --git a/arch/powerpc/include/asm/synch.h b/arch/powerpc/include/asm/synch.h
> index d7cab44..4d97fbe 100644
> --- a/arch/powerpc/include/asm/synch.h
> +++ b/arch/powerpc/include/asm/synch.h
> @@ -37,11 +37,7 @@ static inline void isync(void)
> #ifdef CONFIG_SMP
> -#define __PPC_ACQUIRE_BARRIER \
> - START_LWSYNC_SECTION(97); \
> - isync; \
> - MAKE_LWSYNC_SECTION_ENTRY(97, __lwsync_fixup);
> -#define PPC_ACQUIRE_BARRIER "\n" stringify_in_c(__PPC_ACQUIRE_BARRIER)
> +#define PPC_ACQUIRE_BARRIER "\n" stringify_in_c(sync;)
This can just be done as "\n\tsync\n" instead of the stringify stuff.
More information about the Linuxppc-dev