Commit 08928e7a authored Aug 16, 2012 by Will Deacon Committed by Russell King Aug 25, 2012

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

Commit a76d7bd9 ("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 0bce9c46 ("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>

parent e780c452

arch/arm/include/asm/mutex.h

+7 −2

Original line number	Diff line number	Diff line
		@@ -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 */