On Thu, Apr 17, 2014 at 11:03:55AM -0400, Waiman Long wrote:
> +/**
> + * trylock_pending - try to acquire queue spinlock using the pending bit
> + * @lock : Pointer to queue spinlock structure
> + * @pval : Pointer to value of the queue spinlock 32-bit word
> + * Return: 1 if lock acquired, 0 otherwise
> + */
> +static inline int trylock_pending(struct qspinlock *lock, u32 *pval)
> +{
> + u32 old, new, val = *pval;
I'm not thrilled about you breaking this into a separate function; the
compiler will put it right back and now you get to have that ugly
pointer stuff.
It also makes the function control flow not match the state diagram
anymore.
> +
> + /*
> + * trylock || pending
> + *
> + * 0,0,0 -> 0,0,1 ; trylock
> + * 0,0,1 -> 0,1,1 ; pending
> + */
> + for (;;) {
> + /*
> + * If we observe any contention; queue.
> + */
> + if (val & ~_Q_LOCKED_MASK)
> + return 0;
> +
> + new = _Q_LOCKED_VAL;
> + if (val == new)
> + new |= _Q_PENDING_VAL;
> +
> + old = atomic_cmpxchg(&lock->val, val, new);
> + if (old == val)
> + break;
> +
> + *pval = val = old;
> + }
> +
> + /*
> + * we won the trylock
> + */
> + if (new == _Q_LOCKED_VAL)
> + return 1;
> +
> + /*
> + * we're pending, wait for the owner to go away.
> + *
> + * *,1,1 -> *,1,0
> + */
> + while ((val = atomic_read(&lock->val)) & _Q_LOCKED_MASK)
> + arch_mutex_cpu_relax();
That was a cpu_relax().
> +
> + /*
> + * take ownership and clear the pending bit.
> + *
> + * *,1,0 -> *,0,1
> + */
> + for (;;) {
> + new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL;
> +
> + old = atomic_cmpxchg(&lock->val, val, new);
> + if (old == val)
> + break;
> +
> + val = old;
> + }
> + return 1;
> +}
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