From bae8f567344a7cb6a23ca6e13096ba785c69eb42 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Thu, 15 May 2014 11:00:44 +0200 Subject: s390/spinlock,rwlock: always to a load-and-test first In case a lock is contended it is better to do a load-and-test first before trying to get the lock with compare-and-swap. This helps to avoid unnecessary cache invalidations of the cacheline for the lock if the CPU has to wait for the lock. For an uncontended lock doing the compare-and-swap directly is a bit better, if the CPU does not have the cacheline in its cache yet the compare-and-swap will get it read-write immediately while a load-and-test would get it read-only first. Always to the load-and-test first to avoid the cacheline invalidations for the contended case outweight the potential read-only to read-write cacheline upgrade for the uncontended case. Signed-off-by: Martin Schwidefsky --- arch/s390/include/asm/spinlock.h | 50 ++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 20 deletions(-) (limited to 'arch/s390/include') diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h index 5a0b288..96879f7 100644 --- a/arch/s390/include/asm/spinlock.h +++ b/arch/s390/include/asm/spinlock.h @@ -59,7 +59,9 @@ static inline int arch_spin_is_locked(arch_spinlock_t *lp) static inline int arch_spin_trylock_once(arch_spinlock_t *lp) { - return _raw_compare_and_swap(&lp->lock, 0, SPINLOCK_LOCKVAL); + barrier(); + return likely(arch_spin_value_unlocked(*lp) && + _raw_compare_and_swap(&lp->lock, 0, SPINLOCK_LOCKVAL)); } static inline int arch_spin_tryrelease_once(arch_spinlock_t *lp) @@ -69,20 +71,20 @@ static inline int arch_spin_tryrelease_once(arch_spinlock_t *lp) static inline void arch_spin_lock(arch_spinlock_t *lp) { - if (unlikely(!arch_spin_trylock_once(lp))) + if (!arch_spin_trylock_once(lp)) arch_spin_lock_wait(lp); } static inline void arch_spin_lock_flags(arch_spinlock_t *lp, unsigned long flags) { - if (unlikely(!arch_spin_trylock_once(lp))) + if (!arch_spin_trylock_once(lp)) arch_spin_lock_wait_flags(lp, flags); } static inline int arch_spin_trylock(arch_spinlock_t *lp) { - if (unlikely(!arch_spin_trylock_once(lp))) + if (!arch_spin_trylock_once(lp)) return arch_spin_trylock_retry(lp); return 1; } @@ -128,19 +130,29 @@ extern void _raw_write_lock_wait(arch_rwlock_t *lp); extern void _raw_write_lock_wait_flags(arch_rwlock_t *lp, unsigned long flags); extern int _raw_write_trylock_retry(arch_rwlock_t *lp); +static inline int arch_read_trylock_once(arch_rwlock_t *rw) +{ + unsigned int old = ACCESS_ONCE(rw->lock); + return likely((int) old >= 0 && + _raw_compare_and_swap(&rw->lock, old, old + 1)); +} + +static inline int arch_write_trylock_once(arch_rwlock_t *rw) +{ + unsigned int old = ACCESS_ONCE(rw->lock); + return likely(old == 0 && + _raw_compare_and_swap(&rw->lock, 0, 0x80000000)); +} + static inline void arch_read_lock(arch_rwlock_t *rw) { - unsigned int old; - old = rw->lock & 0x7fffffffU; - if (!_raw_compare_and_swap(&rw->lock, old, old + 1)) + if (!arch_read_trylock_once(rw)) _raw_read_lock_wait(rw); } static inline void arch_read_lock_flags(arch_rwlock_t *rw, unsigned long flags) { - unsigned int old; - old = rw->lock & 0x7fffffffU; - if (!_raw_compare_and_swap(&rw->lock, old, old + 1)) + if (!arch_read_trylock_once(rw)) _raw_read_lock_wait_flags(rw, flags); } @@ -155,13 +167,13 @@ static inline void arch_read_unlock(arch_rwlock_t *rw) static inline void arch_write_lock(arch_rwlock_t *rw) { - if (unlikely(!_raw_compare_and_swap(&rw->lock, 0, 0x80000000))) + if (!arch_write_trylock_once(rw)) _raw_write_lock_wait(rw); } static inline void arch_write_lock_flags(arch_rwlock_t *rw, unsigned long flags) { - if (unlikely(!_raw_compare_and_swap(&rw->lock, 0, 0x80000000))) + if (!arch_write_trylock_once(rw)) _raw_write_lock_wait_flags(rw, flags); } @@ -172,18 +184,16 @@ static inline void arch_write_unlock(arch_rwlock_t *rw) static inline int arch_read_trylock(arch_rwlock_t *rw) { - unsigned int old; - old = rw->lock & 0x7fffffffU; - if (likely(_raw_compare_and_swap(&rw->lock, old, old + 1))) - return 1; - return _raw_read_trylock_retry(rw); + if (!arch_read_trylock_once(rw)) + return _raw_read_trylock_retry(rw); + return 1; } static inline int arch_write_trylock(arch_rwlock_t *rw) { - if (likely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000))) - return 1; - return _raw_write_trylock_retry(rw); + if (!arch_write_trylock_once(rw)) + return _raw_write_trylock_retry(rw); + return 1; } #define arch_read_relax(lock) cpu_relax() -- cgit v1.1