Hi Waiman,
On Thu, Oct 15, 2015 at 06:51:03PM -0400, Waiman Long wrote:
> This patch replaces the cmpxchg() and xchg() calls in the native
> qspinlock code with the more relaxed _acquire or _release versions of
> those calls to enable other architectures to adopt queued spinlocks
> with less memory barrier performance overhead.
>
> Signed-off-by: Waiman Long <waiman.l...@hpe.com>
> ---
> include/asm-generic/qspinlock.h | 9 +++++----
> kernel/locking/qspinlock.c | 29 ++++++++++++++++++++++++-----
> 2 files changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
> index e2aadbc..39e1cb2 100644
> --- a/include/asm-generic/qspinlock.h
> +++ b/include/asm-generic/qspinlock.h
> @@ -12,8 +12,9 @@
> * GNU General Public License for more details.
> *
> * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
> + * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
> *
> - * Authors: Waiman Long <waiman.l...@hp.com>
> + * Authors: Waiman Long <waiman.l...@hpe.com>
> */
> #ifndef __ASM_GENERIC_QSPINLOCK_H
> #define __ASM_GENERIC_QSPINLOCK_H
> @@ -62,7 +63,7 @@ static __always_inline int queued_spin_is_contended(struct
> qspinlock *lock)
> static __always_inline int queued_spin_trylock(struct qspinlock *lock)
> {
> if (!atomic_read(&lock->val) &&
> - (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0))
> + (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0))
> return 1;
> return 0;
> }
> @@ -77,7 +78,7 @@ static __always_inline void queued_spin_lock(struct
> qspinlock *lock)
> {
> u32 val;
>
> - val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL);
> + val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL);
> if (likely(val == 0))
> return;
> queued_spin_lock_slowpath(lock, val);
> @@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct
> qspinlock *lock)
> /*
> * smp_mb__before_atomic() in order to guarantee release semantics
> */
> - smp_mb__before_atomic_dec();
> + smp_mb__before_atomic();
> atomic_sub(_Q_LOCKED_VAL, &lock->val);Just be curious, you don't use atomic_sub_release() here on purpose? Regards, Boqun > } > #endif
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