On Fri, Nov 06, 2015 at 12:54:06PM -0500, Waiman Long wrote:
> >>+static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock
> >>*prev)
> >> {
> >> struct pv_node *pn = (struct pv_node *)node;
> >>+ struct pv_node *pp = (struct pv_node *)prev;
> >> int waitcnt = 0;
> >> int loop;
> >>+ bool wait_early;
> >>
> >> /* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */
> >> for (;; waitcnt++) {
> >>- for (loop = SPIN_THRESHOLD; loop; loop--) {
> >>+ for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
> >> if (READ_ONCE(node->locked))
> >> return;
> >>+ if (pv_wait_early(pp, loop)) {
> >>+ wait_early = true;
> >>+ break;
> >>+ }
> >> cpu_relax();
> >> }
> >>
> >So if prev points to another node, it will never see vcpu_running. Was
> >that fully intended?
>
> I had added code in pv_wait_head_or_lock to set the state appropriately for
> the queue head vCPU.
Yes, but that's the head, for nodes we'll always have halted or hashed.
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