[tip:sched/core] sched/core: Give DCE a fighting chance

[tip-bot for Peter Zijlstra <tipbot@xxxxxxxxx>]

Commit-ID:  e0af32e382bb5d6029c53fa50d5c9a9d3af71faf
Gitweb:     https://git.kernel.org/tip/e0af32e382bb5d6029c53fa50d5c9a9d3af71faf
Author:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 5 Dec 2018 11:23:56 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 21 Jan 2019 11:27:54 +0100

sched/core: Give DCE a fighting chance

All that fancy new Energy-Aware scheduling foo is hidden behind a
static_key, which is awesome if you have the stuff enabled in your
config.

However, when you lack all the prerequisites it doesn't make any sense
to pretend we'll ever actually run this, so provide a little more clue
to the compiler so it can more agressively delete the code.

   text    data     bss     dec     hex filename
  50297     976      96   51369    c8a9 defconfig-build/kernel/sched/fair.o
  49227     944      96   50267    c45b defconfig-build/kernel/sched/fair.o

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c     |  4 ++--
 kernel/sched/sched.h    | 18 +++++++++++++-----
 kernel/sched/topology.c |  2 +-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 385b3de738fd..385725eb3bd6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6607,7 +6607,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 	if (sd_flag & SD_BALANCE_WAKE) {
 		record_wakee(p);
 
-		if (static_branch_unlikely(&sched_energy_present)) {
+		if (sched_energy_enabled()) {
 			new_cpu = find_energy_efficient_cpu(p, prev_cpu);
 			if (new_cpu >= 0)
 				return new_cpu;
@@ -8641,7 +8641,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 	 */
 	update_sd_lb_stats(env, &sds);
 
-	if (static_branch_unlikely(&sched_energy_present)) {
+	if (sched_energy_enabled()) {
 		struct root_domain *rd = env->dst_rq->rd;
 
 		if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d04530bf251f..d27c1a5d4e25 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2299,11 +2299,19 @@ unsigned long scale_irq_capacity(unsigned long util, unsigned long irq, unsigned
 #endif
 
 #if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
+
 #define perf_domain_span(pd) (to_cpumask(((pd)->em_pd->cpus)))
-#else
+
+DECLARE_STATIC_KEY_FALSE(sched_energy_present);
+
+static inline bool sched_energy_enabled(void)
+{
+	return static_branch_unlikely(&sched_energy_present);
+}
+
+#else /* ! (CONFIG_ENERGY_MODEL && CONFIG_CPU_FREQ_GOV_SCHEDUTIL) */
+
 #define perf_domain_span(pd) NULL
-#endif
+static inline bool sched_energy_enabled(void) { return false; }
 
-#ifdef CONFIG_SMP
-extern struct static_key_false sched_energy_present;
-#endif
+#endif /* CONFIG_ENERGY_MODEL && CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 50c3fc316c54..4ae9403420ed 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -201,8 +201,8 @@ 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_STATIC_KEY_FALSE(sched_energy_present);
 unsigned int sysctl_sched_energy_aware = 1;
 DEFINE_MUTEX(sched_energy_mutex);
 bool sched_energy_update;