linux-kernel - [RFCv3 2/8] sched: Introduce switch to enable TurboSched mode

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Date:   Tue, 25 Jun 2019 10:07:20 +0530
From:   Parth Shah <parth@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, dietmar.eggemann@....com,
        patrick.bellasi@....com
Subject: [RFCv3 2/8] sched: Introduce switch to enable TurboSched mode

This patch creates a static key which allows to enable or disable
TurboSched feature at runtime.

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

The patch also provides get/put methods to keep track of the tasks using
the TurboSched feature. 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@...ux.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 19c7204d6351..ef83725bd4b0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -61,6 +61,26 @@ __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 e5599b33ffb8..1f239a960a6d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2426,3 +2426,12 @@ 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