On Tue, 2013-06-11 at 12:49 -0700, Paul E. McKenney wrote:
> +bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc)
> +{
> + if (unlikely(inc.head & 0x1)) {
> +
> + /* This lock has a queue, so go spin on the queue. */
> + if (tkt_q_do_spin(ap, inc))
> + return true;
> +
> + /* Get here if the queue is in transition: Retry next time. */
> +
This looks better, but please add a comment, something to the likes of:
/*
* Only the TKT_Q_SWITCH waiter will set up the queue to prevent
* a thundering herd of setups to occur. It is still possible for
* more than one task to perform a setup if the lock is released
* after this check, a waiter coming in may also match this test. But
* that's covered by the cmpxchg() setup in tkt_q_start_contend.
*/
> + } else if (inc.tail - TKT_Q_SWITCH == inc.head) {
Also shouldn't this be:
} else if ((__ticket_t)(inc.tail - TKT_Q_SWITCH) == inc.head) {
As TKT_Q_SWITCH doesn't have a type, I'm not sure how C will evaluate
this. I always screw type conversions up, and just add in the type casts
to be safe.
You could also give TKT_Q_SWITCH a type too.
-- Steve
> +
> + /*
> + * This lock has lots of spinners, but no queue.
> + * Go create a queue to spin on.
> + */
> + if (tkt_q_start_contend(ap, inc))
> + return true;
> +
> + /* Get here if the queue is in transition: Retry next time. */
> + }
> +
> + /* Either no need for a queue or the queue is in transition. Spin. */
> + return false;
> +}
> +EXPORT_SYMBOL(tkt_spin_pass);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
