Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS

[Peter Zijlstra]

On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote:
> +static __always_inline void
> +clear_pending_set_locked(struct qspinlock *lock, u32 val)
> +{
> +	struct __qspinlock *l = (void *)lock;
> +
> +	ACCESS_ONCE(l->locked_pending) = 1;
> +}

> @@ -157,8 +251,13 @@ static inline int trylock_pending(struct qspinlock *lock, u32 *pval)
>  	 * we're pending, wait for the owner to go away.
>  	 *
>  	 * *,1,1 -> *,1,0
> +	 *
> +	 * this wait loop must be a load-acquire such that we match the
> +	 * store-release that clears the locked bit and create lock
> +	 * sequentiality; this because not all try_clear_pending_set_locked()
> +	 * implementations imply full barriers.

You renamed the function referred in the above comment.

>  	 */
> -	while ((val = atomic_read(&lock->val)) & _Q_LOCKED_MASK)
> +	while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_MASK)
>  		arch_mutex_cpu_relax();
>  
>  	/*
--
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