[RFC PATCH v2 8/8] cpuidle: introduce run queue average idle to make idle prediction

[Aubrey Li]

Introduce run queue average idle in scheduler as a factor to make
idle prediction

Signed-off-by: Aubrey Li <aubrey.li@xxxxxxxxxxxxxxx>
---
 drivers/cpuidle/cpuidle.c | 12 ++++++++++++
 include/linux/cpuidle.h   |  1 +
 kernel/sched/idle.c       |  5 +++++
 3 files changed, 18 insertions(+)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index be56cea..9424a2d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -364,6 +364,18 @@ void cpuidle_predict(void)
 		return;
 	}
 
+	/*
+	 * check scheduler if the coming idle is likely a fast idle
+	 */
+	idle_interval = div_u64(sched_idle_avg(), NSEC_PER_USEC);
+	if (idle_interval < overhead_threshold) {
+		dev->idle_stat.fast_idle = true;
+		return;
+	}
+
+	/*
+	 * check the idle governor if the coming idle is likely a fast idle
+	 */
 	if (cpuidle_curr_governor->predict) {
 		dev->idle_stat.predicted_us = cpuidle_curr_governor->predict();
 		/*
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 45b8264..387d72b 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -234,6 +234,7 @@ static inline void cpuidle_use_deepest_state(bool enable)
 /* kernel/sched/idle.c */
 extern void sched_idle_set_state(struct cpuidle_state *idle_state);
 extern void default_idle_call(void);
+extern u64 sched_idle_avg(void);
 
 #ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
 void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a);
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8704f3c..d23b472 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -30,6 +30,11 @@ void sched_idle_set_state(struct cpuidle_state *idle_state)
 	idle_set_state(this_rq(), idle_state);
 }
 
+u64 sched_idle_avg(void)
+{
+	return this_rq()->avg_idle;
+}
+
 static int __read_mostly cpu_idle_force_poll;
 
 void cpu_idle_poll_ctrl(bool enable)
-- 
2.7.4