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

Aubrey Li
2017-09-30T07:21:41Z

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