linux-kernel - [RFC PATCH v2 3/8] cpuidle: add a new predict interface

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Date:   Sat, 30 Sep 2017 15:20:29 +0800
From:   Aubrey Li <aubrey.li@...el.com>
To:     tglx@...utronix.de, peterz@...radead.org, rjw@...ysocki.net,
        len.brown@...el.com, ak@...ux.intel.com, tim.c.chen@...ux.intel.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...el.com>
Subject: [RFC PATCH v2 3/8] cpuidle: add a new predict interface

For the governor has predict functionality, add a new predict
interface in cpuidle framework to call and use it.
---
 drivers/cpuidle/cpuidle.c        | 34 ++++++++++++++++++++++++++++++++++
 drivers/cpuidle/governors/menu.c |  7 +++++++
 include/linux/cpuidle.h          |  3 +++
 kernel/sched/idle.c              |  1 +
 4 files changed, 45 insertions(+)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 4066308..ef6f7dd 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -336,6 +336,40 @@ void cpuidle_entry_end(void)
 }
 
 /**
+ * cpuidle_predict - predict whether the coming idle is a fast idle or not
+ */
+void cpuidle_predict(void)
+{
+	struct cpuidle_device *dev = cpuidle_get_device();
+	unsigned int overhead_threshold;
+
+	if (!dev)
+		return;
+
+	overhead_threshold = dev->idle_stat.overhead;
+
+	if (cpuidle_curr_governor->predict) {
+		dev->idle_stat.predicted_us = cpuidle_curr_governor->predict();
+		/*
+		 * notify idle governor to avoid reduplicative
+		 * prediction computation
+		 */
+		dev->idle_stat.predicted = true;
+		if (dev->idle_stat.predicted_us < overhead_threshold) {
+			/*
+			 * notify tick subsystem to keep ticking
+			 * for the coming idle
+			 */
+			dev->idle_stat.fast_idle = true;
+		} else
+			dev->idle_stat.fast_idle = false;
+	} else {
+		dev->idle_stat.predicted = false;
+		dev->idle_stat.fast_idle = false;
+	}
+}
+
+/**
  * cpuidle_install_idle_handler - installs the cpuidle idle loop handler
  */
 void cpuidle_install_idle_handler(void)
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 6bed197..90b2a10 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -344,6 +344,12 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (unlikely(latency_req == 0))
 		return 0;
 
+	/*don't predict again if idle framework already did it */
+	if (!dev->idle_stat.predicted)
+		menu_predict();
+	else
+		dev->idle_stat.predicted = false;
+
 	if (CPUIDLE_DRIVER_STATE_START > 0) {
 		struct cpuidle_state *s = &drv->states[CPUIDLE_DRIVER_STATE_START];
 		unsigned int polling_threshold;
@@ -518,6 +524,7 @@ static struct cpuidle_governor menu_governor = {
 	.enable =	menu_enable_device,
 	.select =	menu_select,
 	.reflect =	menu_reflect,
+	.predict =	menu_predict,
 };
 
 /**
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index cad9b71..9ca0288 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -143,6 +143,7 @@ extern int cpuidle_select(struct cpuidle_driver *drv,
 			  struct cpuidle_device *dev);
 extern void cpuidle_entry_start(void);
 extern void cpuidle_entry_end(void);
+extern void cpuidle_predict(void);
 extern int cpuidle_enter(struct cpuidle_driver *drv,
 			 struct cpuidle_device *dev, int index);
 extern void cpuidle_reflect(struct cpuidle_device *dev, int index);
@@ -178,6 +179,7 @@ static inline int cpuidle_select(struct cpuidle_driver *drv,
 {return -ENODEV; }
 static inline void cpuidle_entry_start(void) { }
 static inline void cpuidle_entry_end(void) { }
+static inline void cpuidle_predict(void) { }
 static inline int cpuidle_enter(struct cpuidle_driver *drv,
 				struct cpuidle_device *dev, int index)
 {return -ENODEV; }
@@ -255,6 +257,7 @@ struct cpuidle_governor {
 	int  (*select)		(struct cpuidle_driver *drv,
 					struct cpuidle_device *dev);
 	void (*reflect)		(struct cpuidle_device *dev, int index);
+	unsigned int (*predict)(void);
 };
 
 #ifdef CONFIG_CPU_IDLE
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 0951dac..8704f3c 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -225,6 +225,7 @@ static void do_idle(void)
 	 */
 	__current_set_polling();
 	quiet_vmstat();
+	cpuidle_predict();
 	tick_nohz_idle_enter();
 	cpuidle_entry_end();
 
-- 
2.7.4