sched/rt: Remove unnecessary push for unfit tasks

In task_woken_rt() and switched_to_rto() we try trigger push-pull if the
task is unfit.

But the logic is found lacking because if the task was the only one
running on the CPU, then rt_rq is not in overloaded state and won't
trigger a push.

The necessity of this logic was under a debate as well, a summary of
the discussion can be found in the following thread:

  https://lore.kernel.org/lkml/20200226160247.iqvdakiqbakk2llz@e107158-lin.cambridge.arm.com/

Remove the logic for now until a better approach is agreed upon.

Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware")
Link: https://lkml.kernel.org/r/20200302132721.8353-6-qais.yousef@arm.com

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index bcb143661a86332b09c7073b3110f48d543d0988..df11d88c9895f4c55be0768c5c180ea5c5f8149a 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2225,7 +2225,7 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
                            (rq->curr->nr_cpus_allowed < 2 ||
                             rq->curr->prio <= p->prio);
 
-       if (need_to_push || !rt_task_fits_capacity(p, cpu_of(rq)))
+       if (need_to_push)
                push_rt_tasks(rq);
 }
 
@@ -2297,10 +2297,7 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
         */
        if (task_on_rq_queued(p) && rq->curr != p) {
 #ifdef CONFIG_SMP
-               bool need_to_push = rq->rt.overloaded ||
-                                   !rt_task_fits_capacity(p, cpu_of(rq));
-
-               if (p->nr_cpus_allowed > 1 && need_to_push)
+               if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
                        rt_queue_push_tasks(rq);
 #endif /* CONFIG_SMP */
                if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))