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Commit 78814285 authored by Quentin Perret's avatar Quentin Perret
Browse files

FROMLIST: sched: Introduce sched_energy_present static key 



In order to make sure Energy Aware Scheduling (EAS) will not impact
systems where no Energy Model is available, introduce a static key
guarding the access to EAS code. Since EAS is enabled on a
per-root-domain basis, the static key is enabled when at least one root
domain meets all conditions for EAS.

Change-Id: Ifa3e490e023d3f57b2f1b1272d5ea58d6ae726ab
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarQuentin Perret <quentin.perret@arm.com>
Message-Id: <20181016101513.26919-10-quentin.perret@arm.com>
Signed-off-by: default avatarQuentin Perret <quentin.perret@arm.com>
parent 1e6b1214

kernel/sched/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -2281,3 +2281,7 @@ unsigned long scale_irq_capacity(unsigned long util, unsigned long irq, unsigned 
#else

#define perf_domain_span(pd) NULL

#endif



#ifdef CONFIG_SMP

extern struct static_key_false sched_energy_present;

#endif

kernel/sched/topology.c

+31 −0
Original line number Diff line number Diff line
@@ -201,6 +201,7 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent) 
	return 1;

}



DEFINE_STATIC_KEY_FALSE(sched_energy_present);

#if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)

DEFINE_MUTEX(sched_energy_mutex);

bool sched_energy_update;
@@ -273,6 +274,35 @@ static void destroy_perf_domain_rcu(struct rcu_head *rp) 
	free_pd(pd);

}



static void sched_energy_start(int ndoms_new, cpumask_var_t doms_new[])

{

	/*

	 * The conditions for EAS to start are checked during the creation of

	 * root domains. If one of them meets all conditions, it will have a

	 * non-null list of performance domains.

	 */

	while (ndoms_new) {

		if (cpu_rq(cpumask_first(doms_new[ndoms_new - 1]))->rd->pd)

			goto enable;

		ndoms_new--;

	}



	if (static_branch_unlikely(&sched_energy_present)) {

		if (sched_debug())

			pr_info("%s: stopping EAS\n", __func__);

		static_branch_disable_cpuslocked(&sched_energy_present);

	}



	return;



enable:

	if (!static_branch_unlikely(&sched_energy_present)) {

		if (sched_debug())

			pr_info("%s: starting EAS\n", __func__);

		static_branch_enable_cpuslocked(&sched_energy_present);

	}

}



/*

 * EAS can be used on a root domain if it meets all the following conditions:

 *    1. an Energy Model (EM) is available;
@@ -2187,6 +2217,7 @@ void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[], 
match3:

		;

	}

	sched_energy_start(ndoms_new, doms_new);

#endif



	/* Remember the new sched domains: */