On Mon, Feb 10, 2014 at 01:15:59PM -0800, Jason Low wrote:
> On Mon, 2014-02-10 at 20:58 +0100, Peter Zijlstra wrote:
> > +void osq_unlock(struct optimistic_spin_queue **lock)
> > +{
> > + struct optimistic_spin_queue *node = this_cpu_ptr(&osq_node);
> > + struct optimistic_spin_queue *next;
> > +
> > + /*
> > + * Fast path for the uncontended case.
> > + */
> > + if (likely(cmpxchg(lock, node, NULL) == node))
> > + return;
>
> Can we can also add the following code here as I'm noticing next != NULL
> is the much more likely scenario on my box:
>
> next = xchg(&node->next, NULL);
> if (next) {
> ACCESS_ONCE(next->locked) = 1;
> return;
Is adding that really much faster than the relatively straight path
oqs_wait_next() would walk to bit the same exit?
The only reason I pulled out the above cmpxchg() is because its the
uncontended fast path, which seems like a special enough case.
> > + next = osq_wait_next(lock, node, NULL);
> > + if (next)
> > + ACCESS_ONCE(next->locked) = 1;
> > +}
>
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