Le jeudi 26 mai 2011 Ã 16:16 -0500, Christoph Lameter a Ãcrit :
> Here is a new patch that may address the concerns. The list of cpus that
> support CMPXCHG_DOUBLE is not complete.Could someone help me complete it?
>
>
>
> Subject: x86: Add support for cmpxchg_double
>
> A simple implementation that only supports the word size and does not
> have a fallback mode (would require a spinlock).
>
> And 32 and 64 bit support for cmpxchg_double. cmpxchg double uses
> the cmpxchg8b or cmpxchg16b instruction on x86 processors to compare
> and swap 2 machine words. This allows lockless algorithms to move more
> context information through critical sections.
>
> Set a flag CONFIG_CMPXCHG_DOUBLE to signal the support of that feature
> during kernel builds.
>
> Cc: tj@xxxxxxxxxx
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> ---
> arch/x86/Kconfig.cpu | 10 +++++++
> arch/x86/include/asm/cmpxchg_32.h | 48 ++++++++++++++++++++++++++++++++++++++
> arch/x86/include/asm/cmpxchg_64.h | 45 +++++++++++++++++++++++++++++++++++
> arch/x86/include/asm/cpufeature.h | 1
> 4 files changed, 104 insertions(+)
>
> Index: linux-2.6/arch/x86/include/asm/cmpxchg_64.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/cmpxchg_64.h 2011-05-26 16:03:33.595608967 -0500
> +++ linux-2.6/arch/x86/include/asm/cmpxchg_64.h 2011-05-26 16:06:25.815607865 -0500
> @@ -151,4 +151,49 @@ extern void __cmpxchg_wrong_size(void);
> cmpxchg_local((ptr), (o), (n)); \
> })
>
> +#define cmpxchg16b(ptr, o1, o2, n1, n2) \
> +({ \
> + char __ret; \
> + __typeof__(o2) __junk; \
> + __typeof__(*(ptr)) __old1 = (o1); \
> + __typeof__(o2) __old2 = (o2); \
> + __typeof__(*(ptr)) __new1 = (n1); \
> + __typeof__(o2) __new2 = (n2); \
> + asm volatile(LOCK_PREFIX_HERE "lock; cmpxchg16b (%%rsi);setz %1" \
If there is no emulation, why do you force rsi here ?
It could be something else, like "=m" (*ptr) ?
(same remark for other functions)
> + : "=d"(__junk), "=a"(__ret) \
> + : "S"(ptr), "b"(__new1), "c"(__new2), \
> + "a"(__old1), "d"(__old2)); \
> + __ret; })
> +
> +
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