On Mon, Jul 28, 2014 at 03:56:12PM -0700, Paul E. McKenney wrote:
> + /*
> + * Each pass through the following loop scans the list
> + * of holdout tasks, removing any that are no longer
> + * holdouts. When the list is empty, we are done.
> + */
> + while (!list_empty(&rcu_tasks_holdouts)) {
> + schedule_timeout_interruptible(HZ / 10);
> + flush_signals(current);
> + rcu_read_lock();
> + list_for_each_entry_rcu(t, &rcu_tasks_holdouts,
> + rcu_tasks_holdout_list) {
> + if (smp_load_acquire(&t->rcu_tasks_holdout))
> + continue;
> + list_del_init(&t->rcu_tasks_holdout_list);
> + /* @@@ need to check for usermode on CPU. */
> + }
> + rcu_read_unlock();
> + }
That's a potential CPU runtime sink.. imagine having to scan 100k tasks
10 times a second. Polling O(nr_tasks) is not good.
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