sched: Do eas idle balance regardless of the rq avg idle value

EAS relies on idle balance to migrate a misfit task towards a cpu with
higher capacity.

When such a cpu becomes idle, idle balance should happen even if the rq
avg idle is smaller than the sched migration cost (default 500us).

The rq avg idle is updated during the wakeup of a task in case the rq has
a non-null idle_stamp. This value stays unchanged and valid until the next
task wakes up on this cpu after an idle period.

So rq avg idle could be smaller than sched migration cost preventing the
idle balance from happening. In this case we would be at the mercy of
wakeup, periodic or nohz-idle load balancing to put another task on this
cpu.

To break this dependency towards rq avg idle make EAS idle balance
independent from this rq avg idle has to be larger than sched migration
cost.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 08e2ef16d6001bf6176ff1e976fa899e2c8b7bbe..3c2ddfc8cee8253df00043671e7e27f328f4a8ad 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7793,8 +7793,9 @@ static int idle_balance(struct rq *this_rq)
         */
        this_rq->idle_stamp = rq_clock(this_rq);
 
-       if (this_rq->avg_idle < sysctl_sched_migration_cost ||
-           !this_rq->rd->overload) {
+       if (!energy_aware() &&
+           (this_rq->avg_idle < sysctl_sched_migration_cost ||
+            !this_rq->rd->overload)) {
                rcu_read_lock();
                sd = rcu_dereference_check_sched_domain(this_rq->sd);
                if (sd)