Commit 9d783c8d authored by Vincent Guittot's avatar Vincent Guittot Committed by Peter Zijlstra
Browse files

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: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarTim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20211019123537.17146-3-vincent.guittot@linaro.org
parent 9e9af819

kernel/sched/fair.c

+6 −3
Original line number Diff line number Diff line
@@ -10873,17 +10873,20 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) 
	 */

	rq_unpin_lock(this_rq, rf);



	if (this_rq->avg_idle < sysctl_sched_migration_cost ||

	    !READ_ONCE(this_rq->rd->overload)) {



	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) ||

	    (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {



		if (sd)

			update_next_balance(sd, &next_balance);

		rcu_read_unlock();



		goto out;

	}

	rcu_read_unlock();



	raw_spin_rq_unlock(this_rq);