From ae564c63b8311fa73c21e456e00dba1f4b1ff6bc Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 11 Nov 2008 17:54:15 +0000 Subject: powerpc: Optimise mutex This implements an optimised mutex fastpath for powerpc, making use of acquire and release barrier semantics. This takes the mutex lock+unlock benchmark from 203 to 173 cycles on a G5. Signed-off-by: Nick Piggin Signed-off-by: Paul Mackerras --- arch/powerpc/include/asm/mutex.h | 135 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 130 insertions(+), 5 deletions(-) (limited to 'arch/powerpc/include/asm/mutex.h') diff --git a/arch/powerpc/include/asm/mutex.h b/arch/powerpc/include/asm/mutex.h index 458c1f7fbc18..dabc01c727b8 100644 --- a/arch/powerpc/include/asm/mutex.h +++ b/arch/powerpc/include/asm/mutex.h @@ -1,9 +1,134 @@ /* - * Pull in the generic implementation for the mutex fastpath. + * Optimised mutex implementation of include/asm-generic/mutex-dec.h algorithm + */ +#ifndef _ASM_POWERPC_MUTEX_H +#define _ASM_POWERPC_MUTEX_H + +static inline int __mutex_cmpxchg_lock(atomic_t *v, int old, int new) +{ + int t; + + __asm__ __volatile__ ( +"1: lwarx %0,0,%1 # mutex trylock\n\ + cmpw 0,%0,%2\n\ + bne- 2f\n" + PPC405_ERR77(0,%1) +" stwcx. %3,0,%1\n\ + bne- 1b" + ISYNC_ON_SMP + "\n\ +2:" + : "=&r" (t) + : "r" (&v->counter), "r" (old), "r" (new) + : "cc", "memory"); + + return t; +} + +static inline int __mutex_dec_return_lock(atomic_t *v) +{ + int t; + + __asm__ __volatile__( +"1: lwarx %0,0,%1 # mutex lock\n\ + addic %0,%0,-1\n" + PPC405_ERR77(0,%1) +" stwcx. %0,0,%1\n\ + bne- 1b" + ISYNC_ON_SMP + : "=&r" (t) + : "r" (&v->counter) + : "cc", "memory"); + + return t; +} + +static inline int __mutex_inc_return_unlock(atomic_t *v) +{ + int t; + + __asm__ __volatile__( + LWSYNC_ON_SMP +"1: lwarx %0,0,%1 # mutex unlock\n\ + addic %0,%0,1\n" + PPC405_ERR77(0,%1) +" stwcx. %0,0,%1 \n\ + bne- 1b" + : "=&r" (t) + : "r" (&v->counter) + : "cc", "memory"); + + return t; +} + +/** + * __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 if + * it wasn't 1 originally. This function MUST leave the value lower than + * 1 even when the "1" assertion wasn't true. + */ +static inline void +__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) +{ + if (unlikely(__mutex_dec_return_lock(count) < 0)) + fail_fn(count); +} + +/** + * __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 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(__mutex_dec_return_lock(count) < 0)) + return fail_fn(count); + 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 . + * 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. + */ +static inline void +__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) +{ + if (unlikely(__mutex_inc_return_unlock(count) <= 0)) + fail_fn(count); +} + +#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 * - * TODO: implement optimized primitives instead, or leave the generic - * implementation in place, or pick the atomic_xchg() based generic - * implementation. (see asm-generic/mutex-xchg.h for details) + * Change the count from 1 to 0, and return 1 (success), or if the count + * was not 1, then return 0 (failure). */ +static inline int +__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) +{ + if (likely(__mutex_cmpxchg_lock(count, 1, 0) == 1)) + return 1; + return 0; +} -#include +#endif -- cgit v1.2.3