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Commit 2c7cc326 authored by Joonwoo Park's avatar Joonwoo Park
Browse files

sched: continue to search less power efficient cpu for load balancer 



When choosing a CPU to do power-aware active balance from the load
balancer currently selects the first eligible CPU it finds, even if
there is another eligible CPU which is higher-power. This can lead to
suboptimal load balancing behavior and extra migrations. Power and
performance will be impacted.

Achieve better power and performance by continuing to search the least
power efficient cpu as long as the cpu's load average is higher than or
equal to the busiest cpu found by far.

CRs-fixed: 777341
Change-Id: I14eb21ab725bf7dab88b2e1e169aced6f2d712ca
Signed-off-by: default avatarJoonwoo Park <joonwoop@codeaurora.org>
parent 2a06ffb1

kernel/sched/fair.c

+25 −11
Original line number Diff line number Diff line
@@ -6208,7 +6208,8 @@ static bool update_sd_pick_busiest(struct lb_env *env, 
				   struct sched_group *sg,

				   struct sg_lb_stats *sgs)

{

	int cpu;

	int cpu, cpu_busiest;

	unsigned int pc, pc_busiest;



	if (sched_boost() && !sds->busiest && sgs->sum_nr_running &&

		(env->idle != CPU_NOT_IDLE) && (capacity(env->dst_rq) >
@@ -6217,7 +6218,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, 
		return true;

	}



	if (sgs->avg_load <= sds->max_load)

	if (sgs->avg_load < sds->max_load)

		return false;



	if (sgs->sum_nr_running > sgs->group_capacity) {
@@ -6230,21 +6231,34 @@ static bool update_sd_pick_busiest(struct lb_env *env, 
		return true;

	}



	/* Mark a less power-efficient CPU as busy only if we haven't

	 * seen a busy group yet and we are close to throttling. We want to

	 * prioritize spreading work over power optimization.

	/*

	 * Mark a less power-efficient CPU as busy only we are close to

	 * throttling. We want to prioritize spreading work over power

	 * optimization.

	 */

	cpu = cpumask_first(sched_group_cpus(sg));

	cpu = group_first_cpu(sg);

	if (sysctl_sched_enable_power_aware &&

	    !sds->busiest && (capacity(env->dst_rq) == group_rq_capacity(sg)) &&

	    (!sds->busiest || (env->flags & LBF_PWR_ACTIVE_BALANCE)) &&

	    (capacity(env->dst_rq) == group_rq_capacity(sg)) &&

	    sgs->sum_nr_running && (env->idle != CPU_NOT_IDLE) &&

	    power_cost_at_freq(env->dst_cpu, 0) <

	    power_cost_at_freq(cpu, 0) &&

	    !is_task_migration_throttled(cpu_rq(cpu)->curr) &&

	    is_cpu_throttling_imminent(cpu)) {

		pc = power_cost_at_freq(cpu, 0);

		if (sds->busiest) {

			cpu_busiest = group_first_cpu(sds->busiest);

			pc_busiest = power_cost_at_freq(cpu_busiest, 0);

			if (pc_busiest < pc)

				return true;

		} else {

			if (power_cost_at_freq(env->dst_cpu, 0) < pc) {

				env->flags |= LBF_PWR_ACTIVE_BALANCE;

				return true;

			}

		}

	}



	if (sgs->avg_load == sds->max_load)

		return false;



	/*

	 * ASYM_PACKING needs to move all the work to the lowest