On Tue, Jun 03, 2014 at 12:43:47PM +0200, Peter Zijlstra wrote: > We need rq->curr, rq->idle 'sleeps' with polling set and nr clear, but > it obviously has no effect setting that if its not actually the current > task. > > Touching rq->curr needs holding rcu_read_lock() though, to make sure the > task stays around, still shouldn't be a problem.
> @@ -1581,8 +1604,14 @@ void scheduler_ipi(void)
>
> static void ttwu_queue_remote(struct task_struct *p, int cpu)
> {
> - if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list))
> - smp_send_reschedule(cpu);
> + struct rq *rq = cpu_rq(cpu);
> +
> + if (llist_add(&p->wake_entry, &rq->wake_list)) {
> + rcu_read_lock();
> + if (!set_nr_if_polling(rq->curr))
> + smp_send_reschedule(cpu);
> + rcu_read_unlock();
> + }
> }
Hrmm, I think that is still broken, see how in schedule() we clear NR
before setting the new ->curr.
So I think I had a loop on rq->curr the last time we talked about this,
but alternatively we could look at clearing NR after setting a new curr.
I think I once looked at why it was done before, of course I can't
actually remember the details :/
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