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SubjectRe: [PATCH v9 04/19] qspinlock: Extract out the exchange of tail code word
On Thu, Apr 17, 2014 at 11:03:56AM -0400, Waiman Long wrote:
> @@ -192,36 +220,25 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val)
> node->next = NULL;
>
> /*
> + * We touched a (possibly) cold cacheline; attempt the trylock once
> + * more in the hope someone let go while we weren't watching as long
> + * as no one was queuing.
> */
> + if (!(val & _Q_TAIL_MASK) && queue_spin_trylock(lock))
> + goto release;

But you just did a potentially very expensive op; @val isn't
representative anymore!


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