On 23/10/20 11:12, Peter Zijlstra wrote:
> @@ -7006,15 +7024,20 @@ static bool balance_push(struct rq *rq)
> * Both the cpu-hotplug and stop task are in this case and are
> * required to complete the hotplug process.
> */
> - if (is_per_cpu_kthread(push_task)) {
> + if (is_per_cpu_kthread(push_task) || is_migration_disabled(push_task)) {
is_migration_disabled(p) implies rq_has_pinned_tasks(task_rq(p)), right?
So having a "simple"
if (is_migration_disabled(push_task))
return;
would help simpletons like me trying to read through this.
> /*
> * If this is the idle task on the outgoing CPU try to wake
> * up the hotplug control thread which might wait for the
> * last task to vanish. The rcuwait_active() check is
> * accurate here because the waiter is pinned on this CPU
> * and can't obviously be running in parallel.
> + *
> + * On RT kernels this also has to check whether there are
> + * pinned and scheduled out tasks on the runqueue. They
> + * need to leave the migrate disabled section first.
> */
> - if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) {
> + if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
> + rcuwait_active(&rq->hotplug_wait)) {
> raw_spin_unlock(&rq->lock);
> rcuwait_wake_up(&rq->hotplug_wait);
> raw_spin_lock(&rq->lock);
