linux/arch/arm/include/asm/mutex.h
Will Deacon 08928e7aea ARM: 7495/1: mutex: use generic atomic_dec-based implementation for ARMv6+
Commit a76d7bd96d ("ARM: 7467/1: mutex: use generic xchg-based
implementation for ARMv6+") removed the barrier-less, ARM-specific
mutex implementation in favour of the generic xchg-based code.

Since then, a bug was uncovered in the xchg code when running on SMP
platforms, due to interactions between the locking paths and the
MUTEX_SPIN_ON_OWNER code. This was fixed in 0bce9c46bf ("mutex: place
lock in contended state after fastpath_lock failure"), however, the
atomic_dec-based mutex algorithm is now marginally more efficient for
ARM (~0.5% improvement in hackbench scores on dual A15).

This patch moves ARMv6+ platforms to the atomic_dec-based mutex code.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-08-25 09:22:31 +01:00

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C

/*
* arch/arm/include/asm/mutex.h
*
* ARM optimized mutex locking primitives
*
* Please look into asm-generic/mutex-xchg.h for a formal definition.
*/
#ifndef _ASM_MUTEX_H
#define _ASM_MUTEX_H
/*
* On pre-ARMv6 hardware this results in a swp-based implementation,
* which is the most efficient. For ARMv6+, we have exclusive memory
* accessors and use atomic_dec to avoid the extra xchg operations
* on the locking slowpaths.
*/
#if __LINUX_ARM_ARCH__ < 6
#include <asm-generic/mutex-xchg.h>
#else
#include <asm-generic/mutex-dec.h>
#endif
#endif /* _ASM_MUTEX_H */