diff options
| -rw-r--r-- | include/asm-generic/mutex-dec.h | 110 | ||||
| -rw-r--r-- | include/asm-generic/mutex-null.h | 24 | ||||
| -rw-r--r-- | include/asm-generic/mutex-xchg.h | 117 |
3 files changed, 251 insertions, 0 deletions
diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h new file mode 100644 index 00000000000..74b18cda169 --- /dev/null +++ b/include/asm-generic/mutex-dec.h @@ -0,0 +1,110 @@ +/* + * asm-generic/mutex-dec.h + * + * Generic implementation of the mutex fastpath, based on atomic + * decrement/increment. + */ +#ifndef _ASM_GENERIC_MUTEX_DEC_H +#define _ASM_GENERIC_MUTEX_DEC_H + +/** + * __mutex_fastpath_lock - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fail_fn> if + * it wasn't 1 originally. This function MUST leave the value lower than + * 1 even when the "1" assertion wasn't true. + */ +#define __mutex_fastpath_lock(count, fail_fn) \ +do { \ + if (unlikely(atomic_dec_return(count) < 0)) \ + fail_fn(count); \ + else \ + smp_mb(); \ +} while (0) + +/** + * __mutex_fastpath_lock_retval - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fail_fn> if + * it wasn't 1 originally. This function returns 0 if the fastpath succeeds, + * or anything the slow path function returns. + */ +static inline int +__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) +{ + if (unlikely(atomic_dec_return(count) < 0)) + return fail_fn(count); + else { + smp_mb(); + return 0; + } +} + +/** + * __mutex_fastpath_unlock - try to promote the count from 0 to 1 + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 0 + * + * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>. + * In the failure case, this function is allowed to either set the value to + * 1, or to set it to a value lower than 1. + * + * If the implementation sets it to a value of lower than 1, then the + * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs + * to return 0 otherwise. + */ +#define __mutex_fastpath_unlock(count, fail_fn) \ +do { \ + smp_mb(); \ + if (unlikely(atomic_inc_return(count) <= 0)) \ + fail_fn(count); \ +} while (0) + +#define __mutex_slowpath_needs_to_unlock() 1 + +/** + * __mutex_fastpath_trylock - try to acquire the mutex, without waiting + * + * @count: pointer of type atomic_t + * @fail_fn: fallback function + * + * Change the count from 1 to a value lower than 1, and return 0 (failure) + * if it wasn't 1 originally, or return 1 (success) otherwise. This function + * MUST leave the value lower than 1 even when the "1" assertion wasn't true. + * Additionally, if the value was < 0 originally, this function must not leave + * it to 0 on failure. + * + * If the architecture has no effective trylock variant, it should call the + * <fail_fn> spinlock-based trylock variant unconditionally. + */ +static inline int +__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) +{ + /* + * We have two variants here. The cmpxchg based one is the best one + * because it never induce a false contention state. It is included + * here because architectures using the inc/dec algorithms over the + * xchg ones are much more likely to support cmpxchg natively. + * + * If not we fall back to the spinlock based variant - that is + * just as efficient (and simpler) as a 'destructive' probing of + * the mutex state would be. + */ +#ifdef __HAVE_ARCH_CMPXCHG + if (likely(atomic_cmpxchg(count, 1, 0)) == 1) { + smp_mb(); + return 1; + } + return 0; +#else + return fail_fn(count); +#endif +} + +#endif diff --git a/include/asm-generic/mutex-null.h b/include/asm-generic/mutex-null.h new file mode 100644 index 00000000000..5cf8b7ce0c4 --- /dev/null +++ b/include/asm-generic/mutex-null.h @@ -0,0 +1,24 @@ +/* + * asm-generic/mutex-null.h + * + * Generic implementation of the mutex fastpath, based on NOP :-) + * + * This is used by the mutex-debugging infrastructure, but it can also + * be used by architectures that (for whatever reason) want to use the + * spinlock based slowpath. + */ +#ifndef _ASM_GENERIC_MUTEX_NULL_H +#define _ASM_GENERIC_MUTEX_NULL_H + +/* extra parameter only needed for mutex debugging: */ +#ifndef __IP__ +# define __IP__ +#endif + +#define __mutex_fastpath_lock(count, fail_fn) fail_fn(count __RET_IP__) +#define __mutex_fastpath_lock_retval(count, fail_fn) fail_fn(count __RET_IP__) +#define __mutex_fastpath_unlock(count, fail_fn) fail_fn(count __RET_IP__) +#define __mutex_fastpath_trylock(count, fail_fn) fail_fn(count) +#define __mutex_slowpath_needs_to_unlock() 1 + +#endif diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h new file mode 100644 index 00000000000..1d24f47e6c4 --- /dev/null +++ b/include/asm-generic/mutex-xchg.h @@ -0,0 +1,117 @@ +/* + * asm-generic/mutex-xchg.h + * + * Generic implementation of the mutex fastpath, based on xchg(). + * + * NOTE: An xchg based implementation is less optimal than an atomic + * decrement/increment based implementation. If your architecture + * has a reasonable atomic dec/inc then you should probably use + * asm-generic/mutex-dec.h instead, or you could open-code an + * optimized version in asm/mutex.h. + */ +#ifndef _ASM_GENERIC_MUTEX_XCHG_H +#define _ASM_GENERIC_MUTEX_XCHG_H + +/** + * __mutex_fastpath_lock - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fail_fn> if it + * wasn't 1 originally. This function MUST leave the value lower than 1 + * even when the "1" assertion wasn't true. + */ +#define __mutex_fastpath_lock(count, fail_fn) \ +do { \ + if (unlikely(atomic_xchg(count, 0) != 1)) \ + fail_fn(count); \ + else \ + smp_mb(); \ +} while (0) + + +/** + * __mutex_fastpath_lock_retval - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fail_fn> if it + * wasn't 1 originally. This function returns 0 if the fastpath succeeds, + * or anything the slow path function returns + */ +static inline int +__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) +{ + if (unlikely(atomic_xchg(count, 0) != 1)) + return fail_fn(count); + else { + smp_mb(); + return 0; + } +} + +/** + * __mutex_fastpath_unlock - try to promote the mutex from 0 to 1 + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 0 + * + * try to promote the mutex from 0 to 1. if it wasn't 0, call <function> + * In the failure case, this function is allowed to either set the value to + * 1, or to set it to a value lower than one. + * If the implementation sets it to a value of lower than one, the + * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs + * to return 0 otherwise. + */ +#define __mutex_fastpath_unlock(count, fail_fn) \ +do { \ + smp_mb(); \ + if (unlikely(atomic_xchg(count, 1) != 0)) \ + fail_fn(count); \ +} while (0) + +#define __mutex_slowpath_needs_to_unlock() 0 + +/** + * __mutex_fastpath_trylock - try to acquire the mutex, without waiting + * + * @count: pointer of type atomic_t + * @fail_fn: spinlock based trylock implementation + * + * Change the count from 1 to a value lower than 1, and return 0 (failure) + * if it wasn't 1 originally, or return 1 (success) otherwise. This function + * MUST leave the value lower than 1 even when the "1" assertion wasn't true. + * Additionally, if the value was < 0 originally, this function must not leave + * it to 0 on failure. + * + * If the architecture has no effective trylock variant, it should call the + * <fail_fn> spinlock-based trylock variant unconditionally. + */ +static inline int +__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) +{ + int prev = atomic_xchg(count, 0); + + if (unlikely(prev < 0)) { + /* + * The lock was marked contended so we must restore that + * state. If while doing so we get back a prev value of 1 + * then we just own it. + * + * [ In the rare case of the mutex going to 1, to 0, to -1 + * and then back to 0 in this few-instructions window, + * this has the potential to trigger the slowpath for the + * owner's unlock path needlessly, but that's not a problem + * in practice. ] + */ + prev = atomic_xchg(count, prev); + if (prev < 0) + prev = 0; + } + smp_mb(); + + return prev; +} + +#endif |