linux-kernel - Re: [patch 17/23] Add cmpxchg

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Date:	Mon, 13 Aug 2007 10:35:01 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Christoph Lameter <clameter@....com>, schwidefsky@...ibm.com,
	linux390@...ibm.com
Subject: Re: [patch 17/23] Add cmpxchg_local to s390

On Sun, Aug 12, 2007 at 10:54:51AM -0400, Mathieu Desnoyers wrote:
> Use the standard __cmpxchg for every type that can be updated atomically.
> Use the new generic cmpxchg_local (disables interrupt) for other types.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> CC: clameter@....com
> CC: schwidefsky@...ibm.com
> CC: linux390@...ibm.com
> ---
>  include/asm-s390/system.h |   34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> Index: linux-2.6-lttng/include/asm-s390/system.h
> ===================================================================
> --- linux-2.6-lttng.orig/include/asm-s390/system.h	2007-08-10 16:16:21.000000000 -0400
> +++ linux-2.6-lttng/include/asm-s390/system.h	2007-08-10 19:35:46.000000000 -0400
> @@ -353,6 +353,40 @@ __cmpxchg(volatile void *ptr, unsigned l
> 
>  #include <linux/irqflags.h>
> 
> +#include <asm-generic/cmpxchg-local.h>
> +
> +static inline unsigned long __cmpxchg_local(volatile void *ptr,
> +				      unsigned long old,
> +				      unsigned long new, int size)
> +{
> +	switch (size) {
> +	case 1:
> +	case 2:
> +	case 4:
> +#ifdef __s390x__
> +	case 8:
> +#endif
> +		return __cmpxchg(ptr, old, new, size);
> +	default:
> +		return __cmpxchg_local_generic(ptr, old, new, size);
> +	}
> +
> +	return old;
> +}
> +
> +/*
> + * cmpxchg_local and cmpxchg64_local are atomic wrt current CPU. Always make
> + * them available.
> + */
> +#define cmpxchg_local(ptr,o,n)						\
> +     (__typeof__(*(ptr)))__cmpxchg_local((ptr), (unsigned long)(o),	\
> +			   	 (unsigned long)(n), sizeof(*(ptr)))
> +#ifdef __s390x__
> +#define cmpxchg64_local(ptr,o,n) cmpxchg_local((ptr),(o),(n))
> +#else
> +#define cmpxchg64_local(ptr,o,n) __cmpxchg64_local_generic((ptr), (o), (n))
> +#endif
> +

What's the reason to have cmpxchg64_local on 32 bit architectures?
Without that need all this would just be a few simple defines.
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