From 08928e7aea930e6822ce8f1b20068bf857ecf20d Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 16 Aug 2012 18:43:04 +0100 Subject: [PATCH] ARM: 7495/1: mutex: use generic atomic_dec-based implementation for ARMv6+ Commit a76d7bd96d65 ("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 0bce9c46bf3b ("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 Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/include/asm/mutex.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/arm/include/asm/mutex.h b/arch/arm/include/asm/mutex.h index b1479fd..87c0449 100644 --- a/arch/arm/include/asm/mutex.h +++ b/arch/arm/include/asm/mutex.h @@ -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 +#else +#include #endif +#endif /* _ASM_MUTEX_H */ -- 2.7.4