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ARM: 7495/1: mutex: use generic atomic_dec-based implementation for ARMv6+

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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>
This commit is contained in:
Will Deacon 2012-08-16 18:43:04 +01:00 committed by Russell King
parent e780c452cf
commit 08928e7aea
1 changed files with 7 additions and 2 deletions
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9
arch/arm/include/asm/mutex.h
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@ -9,8 +9,13 @@
#define _ASM_MUTEX_H
/*
* On pre-ARMv6 hardware this results in a swp-based implementation,
* which is the most efficient. For ARMv6+, we emit a pair of exclusive
* accesses instead.
* 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 */