On Tue, Feb 25, 2014 at 11:56:19AM -0800, Jason Low wrote:
> On Mon, 2014-02-10 at 20:58 +0100, Peter Zijlstra wrote:
>
> > +unqueue:
> > + /*
> > + * Step - A -- stabilize @prev
> > + *
> > + * Undo our @prev->next assignment; this will make @prev's
> > + * unlock()/unqueue() wait for a next pointer since @lock points to us
> > + * (or later).
> > + */
> > +
> > + for (;;) {
> > + if (prev->next == node &&
> > + cmpxchg(&prev->next, node, NULL) == node)
> > + break;
> > +
> > + /*
> > + * We can only fail the cmpxchg() racing against an unlock(),
> > + * in which case we should observe @node->locked becomming
> > + * true.
> > + */
> > + if (smp_load_acquire(&node->locked))
> > + return true;
I've stuck on in right about here. So that we don't unduly delay the
cmpxchg() after the load of prev.
> > +
> > + /*
> > + * Or we race against a concurrent unqueue()'s step-B, in which
> > + * case its step-C will write us a new @node->prev pointer.
> > + */
> > + prev = ACCESS_ONCE(node->prev);
>
> Should we also add an arch_mutex_cpu_relax() to this loop?
>
>
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