lkml.org 
[lkml]   [2011]   [Sep]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers
From
[+linuxppc-dev]

On Tue, Sep 6, 2011 at 11:00 AM, Paul E. McKenney
<paulmck@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
beyond it.

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)
>  #endif
>
>  #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.


-Olof
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-09-09 19:55    [W:0.251 / U:25.124 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site