[RFC v4 2/8] sched: Introduce switch to enable TurboSched mode

[Parth Shah <parth@linux.ibm.com>]

Create a static key which allows to enable or disable TurboSched feature at
runtime.

This key is added in order to enable the TurboSched feature only when
required. This helps in optimizing the scheduler fast-path when the
TurboSched feature is disabled.

Also provide get/put methods to keep track of the tasks using the
TurboSched feature and also refcount jitter tasks. This allows to enable
the feature on setting first task classified as jitter, similarly disable
the feature on unsetting of such last task.

Signed-off-by: Parth Shah <parth@linux.ibm.com>
---
 kernel/sched/core.c  | 20 ++++++++++++++++++++
 kernel/sched/sched.h |  9 +++++++++
 2 files changed, 29 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e7cda4aa8696..ee5980b4e150 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -72,6 +72,26 @@ __read_mostly int scheduler_running;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+DEFINE_STATIC_KEY_FALSE(__turbo_sched_enabled);
+static DEFINE_MUTEX(turbo_sched_lock);
+static int turbo_sched_count;
+
+void turbo_sched_get(void)
+{
+	mutex_lock(&turbo_sched_lock);
+	if (!turbo_sched_count++)
+		static_branch_enable(&__turbo_sched_enabled);
+	mutex_unlock(&turbo_sched_lock);
+}
+
+void turbo_sched_put(void)
+{
+	mutex_lock(&turbo_sched_lock);
+	if (!--turbo_sched_count)
+		static_branch_disable(&__turbo_sched_enabled);
+	mutex_unlock(&turbo_sched_lock);
+}
+
 /*
  * __task_rq_lock - lock the rq @p resides on.
  */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 802b1f3405f2..4a0b90ea8652 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2423,3 +2423,12 @@ static inline bool sched_energy_enabled(void)
 static inline bool sched_energy_enabled(void) { return false; }
 
 #endif /* CONFIG_ENERGY_MODEL && CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
+
+void turbo_sched_get(void);
+void turbo_sched_put(void);
+DECLARE_STATIC_KEY_FALSE(__turbo_sched_enabled);
+
+static inline bool is_turbosched_enabled(void)
+{
+	return static_branch_unlikely(&__turbo_sched_enabled);
+}
-- 
2.17.1