Commit e60b56e4 authored by Vincent Guittot's avatar Vincent Guittot Committed by Peter Zijlstra
Browse files

sched/fair: Wait before decaying max_newidle_lb_cost 



Decay max_newidle_lb_cost only when it has not been updated for a while
and ensure to not decay a recently changed value.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
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/20211019123537.17146-4-vincent.guittot@linaro.org
parent 9d783c8d

include/linux/sched/topology.h

+1 −1
Original line number Diff line number Diff line
@@ -105,7 +105,7 @@ struct sched_domain { 


	/* idle_balance() stats */

	u64 max_newidle_lb_cost;

	unsigned long next_decay_max_lb_cost;

	unsigned long last_decay_max_lb_cost;



	u64 avg_scan_cost;		/* select_idle_sibling */

kernel/sched/fair.c

+27 −9
Original line number Diff line number Diff line
@@ -10239,6 +10239,30 @@ void update_max_interval(void) 
	max_load_balance_interval = HZ*num_online_cpus()/10;

}



static inline bool update_newidle_cost(struct sched_domain *sd, u64 cost)

{

	if (cost > sd->max_newidle_lb_cost) {

		/*

		 * Track max cost of a domain to make sure to not delay the

		 * next wakeup on the CPU.

		 */

		sd->max_newidle_lb_cost = cost;

		sd->last_decay_max_lb_cost = jiffies;

	} else if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) {

		/*

		 * Decay the newidle max times by ~1% per second to ensure that

		 * it is not outdated and the current max cost is actually

		 * shorter.

		 */

		sd->max_newidle_lb_cost = (sd->max_newidle_lb_cost * 253) / 256;

		sd->last_decay_max_lb_cost = jiffies;



		return true;

	}



	return false;

}



/*

 * It checks each scheduling domain to see if it is due to be balanced,

 * and initiates a balancing operation if so.
@@ -10262,14 +10286,9 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle) 
	for_each_domain(cpu, sd) {

		/*

		 * Decay the newidle max times here because this is a regular

		 * visit to all the domains. Decay ~1% per second.

		 * visit to all the domains.

		 */

		if (time_after(jiffies, sd->next_decay_max_lb_cost)) {

			sd->max_newidle_lb_cost =

				(sd->max_newidle_lb_cost * 253) / 256;

			sd->next_decay_max_lb_cost = jiffies + HZ;

			need_decay = 1;

		}

		need_decay = update_newidle_cost(sd, 0);

		max_cost += sd->max_newidle_lb_cost;



		/*
@@ -10911,8 +10930,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) 


			t1 = sched_clock_cpu(this_cpu);

			domain_cost = t1 - t0;

			if (domain_cost > sd->max_newidle_lb_cost)

				sd->max_newidle_lb_cost = domain_cost;

			update_newidle_cost(sd, domain_cost);



			curr_cost += domain_cost;

			t0 = t1;

kernel/sched/topology.c

+1 −1
Original line number Diff line number Diff line
@@ -1568,7 +1568,7 @@ sd_init(struct sched_domain_topology_level *tl, 
		.last_balance		= jiffies,

		.balance_interval	= sd_weight,

		.max_newidle_lb_cost	= 0,

		.next_decay_max_lb_cost	= jiffies,

		.last_decay_max_lb_cost	= jiffies,

		.child			= child,

#ifdef CONFIG_SCHED_DEBUG

		.name			= tl->name,