On Mon, 2013-04-15 at 10:37 -0400, Waiman Long wrote:
[...]
> +typedef struct mspin_node {
> + struct mspin_node *next;
> + int locked; /* 1 if lock acquired */
> +} mspin_node_t;
> +
> +typedef mspin_node_t *mspin_lock_t;
I think we could do without the typedefs, specially mspin_lock_t.
> +
> +#define MLOCK(mutex) ((mspin_lock_t *)&((mutex)->spin_mlock))
> +
> +static noinline void mspin_lock(mspin_lock_t *lock, mspin_node_t *node)
> +{
> + mspin_node_t *prev;
> +
> + /* Init node */
> + node->locked = 0;
> + node->next = NULL;
> +
> + prev = xchg(lock, node);
> + if (likely(prev == NULL)) {
> + /* Lock acquired */
> + node->locked = 1;
> + return;
> + }
> + ACCESS_ONCE(prev->next) = node;
> + smp_wmb();
> + /* Wait until the lock holder passes the lock down */
> + while (!ACCESS_ONCE(node->locked))
> + arch_mutex_cpu_relax();
> +}
> +
> +static void mspin_unlock(mspin_lock_t *lock, mspin_node_t *node)
> +{
> + mspin_node_t *next = ACCESS_ONCE(node->next);
> +
> + if (likely(!next)) {
> + /*
> + * Release the lock by setting it to NULL
> + */
> + if (cmpxchg(lock, node, NULL) == node)
> + return;
> + /* Wait until the next pointer is set */
> + while (!(next = ACCESS_ONCE(node->next)))
> + arch_mutex_cpu_relax();
> + }
> + barrier();
> + ACCESS_ONCE(next->locked) = 1;
> + smp_wmb();
Do we really need the compiler barrier call? The CPUs can reorder
anyway. I assume the smp_wbm() call makes sure no there's no funny
business before the next lock is acquired, might be worth commenting.
Thanks,
Davidlohr
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