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x86: Add support for cmpxchg_double

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A simple implementation that only supports the word size and does not
have a fallback mode (would require a spinlock).

Add 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 that support for double word
cmpxchg detection has been build into the kernel. Note that each subsystem
using cmpxchg_double has to implement a fall back mechanism as long as
we offer support for processors that do not implement cmpxchg_double.

Reviewed-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Christoph Lameter <cl@linux.com>
Link: http://lkml.kernel.org/r/20110601172614.173427964@linux.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Christoph Lameter
2011-06-01 12:25:47 -05:00
committed by H. Peter Anvin
parent 5629937872
commit 3824abd127
4 changed files with 98 additions and 0 deletions
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48
arch/x86/include/asm/cmpxchg_32.h
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@@ -280,4 +280,52 @@ static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
#endif
#define cmpxchg8b(ptr, o1, o2, n1, n2) \
({ \
char __ret; \
__typeof__(o2) __dummy; \
__typeof__(*(ptr)) __old1 = (o1); \
__typeof__(o2) __old2 = (o2); \
__typeof__(*(ptr)) __new1 = (n1); \
__typeof__(o2) __new2 = (n2); \
asm volatile(LOCK_PREFIX "cmpxchg8b %2; setz %1" \
: "=d"(__dummy), "=a" (__ret), "+m" (*ptr)\
: "a" (__old1), "d"(__old2), \
"b" (__new1), "c" (__new2) \
: "memory"); \
__ret; })
#define cmpxchg8b_local(ptr, o1, o2, n1, n2) \
({ \
char __ret; \
__typeof__(o2) __dummy; \
__typeof__(*(ptr)) __old1 = (o1); \
__typeof__(o2) __old2 = (o2); \
__typeof__(*(ptr)) __new1 = (n1); \
__typeof__(o2) __new2 = (n2); \
asm volatile("cmpxchg8b %2; setz %1" \
: "=d"(__dummy), "=a"(__ret), "+m" (*ptr)\
: "a" (__old), "d"(__old2), \
"b" (__new1), "c" (__new2), \
: "memory"); \
__ret; })
#define cmpxchg_double(ptr, o1, o2, n1, n2) \
({ \
BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
VM_BUG_ON((unsigned long)(ptr) % 8); \
cmpxchg8b((ptr), (o1), (o2), (n1), (n2)); \
})
#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
({ \
BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
VM_BUG_ON((unsigned long)(ptr) % 8); \
cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
})
#define system_has_cmpxchg_double() cpu_has_cx8
#endif /* _ASM_X86_CMPXCHG_32_H */