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linux-sg2042/arch/arm/include/asm/mutex.h

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[PATCH] mutex subsystem, add include/asm-arm/mutex.h add the ARM version of mutex.h, which is optimized in assembly for ARMv6, and uses the xchg implementation on pre-ARMv6. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-01-10 07:59:18 +08:00
/*
[ARM] move include/asm-arm to arch/arm/include/asm Move platform independent header files to arch/arm/include/asm, leaving those in asm/arch* and asm/plat* alone. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2008-08-02 17:55:55 +08:00
* arch/arm/include/asm/mutex.h
[PATCH] mutex subsystem, add include/asm-arm/mutex.h add the ARM version of mutex.h, which is optimized in assembly for ARMv6, and uses the xchg implementation on pre-ARMv6. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-01-10 07:59:18 +08:00
*
* 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
/*
ARM: 7467/1: mutex: use generic xchg-based implementation for ARMv6+ The open-coded mutex implementation for ARMv6+ cores suffers from a severe lack of barriers, so in the uncontended case we don't actually protect any accesses performed during the critical section. Furthermore, the code is largely a duplication of the ARMv6+ atomic_dec code but optimised to remove a branch instruction, as the mutex fastpath was previously inlined. Now that this is executed out-of-line, we can reuse the atomic access code for the locking (in fact, we use the xchg code as this produces shorter critical sections). This patch uses the generic xchg based implementation for mutexes on ARMv6+, which introduces barriers to the lock/unlock operations and also has the benefit of removing a fair amount of inline assembly code. Cc: <stable@vger.kernel.org> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Nicolas Pitre <nico@linaro.org> Reported-by: Shan Kang <kangshan0910@gmail.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-07-14 02:15:40 +08:00
* On pre-ARMv6 hardware this results in a swp-based implementation,
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 <nico@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-08-17 01:43:04 +08:00
* 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.
[PATCH] mutex subsystem, add include/asm-arm/mutex.h add the ARM version of mutex.h, which is optimized in assembly for ARMv6, and uses the xchg implementation on pre-ARMv6. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-01-10 07:59:18 +08:00
*/
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 <nico@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-08-17 01:43:04 +08:00
#if __LINUX_ARM_ARCH__ < 6
ARM: 7467/1: mutex: use generic xchg-based implementation for ARMv6+ The open-coded mutex implementation for ARMv6+ cores suffers from a severe lack of barriers, so in the uncontended case we don't actually protect any accesses performed during the critical section. Furthermore, the code is largely a duplication of the ARMv6+ atomic_dec code but optimised to remove a branch instruction, as the mutex fastpath was previously inlined. Now that this is executed out-of-line, we can reuse the atomic access code for the locking (in fact, we use the xchg code as this produces shorter critical sections). This patch uses the generic xchg based implementation for mutexes on ARMv6+, which introduces barriers to the lock/unlock operations and also has the benefit of removing a fair amount of inline assembly code. Cc: <stable@vger.kernel.org> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Nicolas Pitre <nico@linaro.org> Reported-by: Shan Kang <kangshan0910@gmail.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-07-14 02:15:40 +08:00
#include <asm-generic/mutex-xchg.h>
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 <nico@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-08-17 01:43:04 +08:00
#else
#include <asm-generic/mutex-dec.h>
[PATCH] mutex subsystem, add include/asm-arm/mutex.h add the ARM version of mutex.h, which is optimized in assembly for ARMv6, and uses the xchg implementation on pre-ARMv6. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-01-10 07:59:18 +08:00
#endif
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 <nico@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2012-08-17 01:43:04 +08:00
#endif /* _ASM_MUTEX_H */