sched/fair: Skip update_blocked_averages if we are defering load balance

In newidle_balance(), the scheduler skips load balance to the new idle cpu
when the 1st sd of this_rq is:

   this_rq->avg_idle < sd->max_newidle_lb_cost

Doing a costly call to update_blocked_averages() will not be useful and
simply adds overhead when this condition is true.

Check the condition early in newidle_balance() to skip
update_blocked_averages() when possible.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20211019123537.17146-3-vincent.guittot@linaro.org

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c014567..c4c3686 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10873,17 +10873,20 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
         */
        rq_unpin_lock(this_rq, rf);
 
+       rcu_read_lock();
+       sd = rcu_dereference_check_sched_domain(this_rq->sd);
+
        if (this_rq->avg_idle < sysctl_sched_migration_cost ||
-           !READ_ONCE(this_rq->rd->overload)) {
+           !READ_ONCE(this_rq->rd->overload) ||
+           (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
 
-               rcu_read_lock();
-               sd = rcu_dereference_check_sched_domain(this_rq->sd);
                if (sd)
                        update_next_balance(sd, &next_balance);
                rcu_read_unlock();
 
                goto out;
        }
+       rcu_read_unlock();
 
        raw_spin_rq_unlock(this_rq);