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Subject[PATCH v10 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 | 28 ++++++++++++++++++++++++----
2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 6236081d68bf..8decb3bc0e3f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2298,3 +2298,7 @@ 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 70492d4bfed6..24d211ca384d 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 +274,19 @@ static void destroy_perf_domain_rcu(struct rcu_head *rp)
free_pd(pd);
}

+static void sched_energy_set(bool has_eas)
+{
+ if (!has_eas && static_branch_unlikely(&sched_energy_present)) {
+ if (sched_debug())
+ pr_info("%s: stopping EAS\n", __func__);
+ static_branch_disable_cpuslocked(&sched_energy_present);
+ } else if (has_eas && !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;
@@ -299,7 +313,7 @@ static void destroy_perf_domain_rcu(struct rcu_head *rp)
#define EM_MAX_COMPLEXITY 2048

extern struct cpufreq_governor schedutil_gov;
-static void build_perf_domains(const struct cpumask *cpu_map)
+static bool build_perf_domains(const struct cpumask *cpu_map)
{
int i, nr_pd = 0, nr_cs = 0, nr_cpus = cpumask_weight(cpu_map);
struct perf_domain *pd = NULL, *tmp;
@@ -365,7 +379,7 @@ static void build_perf_domains(const struct cpumask *cpu_map)
if (tmp)
call_rcu(&tmp->rcu, destroy_perf_domain_rcu);

- return;
+ return !!pd;

free:
free_pd(pd);
@@ -373,6 +387,8 @@ static void build_perf_domains(const struct cpumask *cpu_map)
rcu_assign_pointer(rd->pd, NULL);
if (tmp)
call_rcu(&tmp->rcu, destroy_perf_domain_rcu);
+
+ return false;
}
#else
static void free_pd(struct perf_domain *pd) { }
@@ -2116,6 +2132,7 @@ static int dattrs_equal(struct sched_domain_attr *cur, int idx_cur,
void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
struct sched_domain_attr *dattr_new)
{
+ bool __maybe_unused has_eas = false;
int i, j, n;
int new_topology;

@@ -2179,14 +2196,17 @@ void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
for (i = 0; i < ndoms_new; i++) {
for (j = 0; j < n && !sched_energy_update; j++) {
if (cpumask_equal(doms_new[i], doms_cur[j]) &&
- cpu_rq(cpumask_first(doms_cur[j]))->rd->pd)
+ cpu_rq(cpumask_first(doms_cur[j]))->rd->pd) {
+ has_eas = true;
goto match3;
+ }
}
/* No match - add perf. domains for a new rd */
- build_perf_domains(doms_new[i]);
+ has_eas |= build_perf_domains(doms_new[i]);
match3:
;
}
+ sched_energy_set(has_eas);
#endif

/* Remember the new sched domains: */
--
2.19.2
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