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Subject[PATCH v8 09/15] sched: Introduce sched_energy_present static key
Date
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.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
---
kernel/sched/sched.h | 4 ++++
kernel/sched/topology.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index cba77f619e4e..9d6cf58a8aff 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2278,3 +2278,7 @@ 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
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8f5efab1c058..58bfda46ac07 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -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: */
--
2.19.1
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