Re: [Xen-devel] [PATCH v9 04/19] qspinlock: Extract out the exchange of tail code word

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

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!

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel