[RFC PATCH v2 4/8] tick/nohz: keep tick on for a fast idle

[Aubrey Li]

If the next idle is expected to be a fast idle, we should keep tick
on before going into idle

Signed-off-by: Aubrey Li <aubrey.li@xxxxxxxxxxxxxxx>
---
 drivers/cpuidle/cpuidle.c | 14 ++++++++++++++
 include/linux/cpuidle.h   |  2 ++
 kernel/time/tick-sched.c  |  4 ++++
 3 files changed, 20 insertions(+)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index ef6f7dd..6cb7e17 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -370,6 +370,20 @@ void cpuidle_predict(void)
 }
 
 /**
+ * cpuidle_fast_idle - predict whether or not the coming idle is a fast idle
+ * This function can be called in irq exit path, make it as soon as possible
+ */
+bool cpuidle_fast_idle(void)
+{
+	struct cpuidle_device *dev = cpuidle_get_device();
+
+	if (!dev)
+		return false;
+
+	return dev->idle_stat.fast_idle;
+}
+
+/**
  * cpuidle_install_idle_handler - installs the cpuidle idle loop handler
  */
 void cpuidle_install_idle_handler(void)
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 9ca0288..791db15 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -144,6 +144,7 @@ extern int cpuidle_select(struct cpuidle_driver *drv,
 extern void cpuidle_entry_start(void);
 extern void cpuidle_entry_end(void);
 extern void cpuidle_predict(void);
+extern bool cpuidle_fast_idle(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);
@@ -180,6 +181,7 @@ static inline int cpuidle_select(struct cpuidle_driver *drv,
 static inline void cpuidle_entry_start(void) { }
 static inline void cpuidle_entry_end(void) { }
 static inline void cpuidle_predict(void) { }
+static inline void cpuidle_fast_idle(void) {return false; }
 static inline int cpuidle_enter(struct cpuidle_driver *drv,
 				struct cpuidle_device *dev, int index)
 {return -ENODEV; }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c7a899c..d663fab 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -27,6 +27,7 @@
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
 #include <linux/context_tracking.h>
+#include <linux/cpuidle.h>
 
 #include <asm/irq_regs.h>
 
@@ -916,6 +917,9 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 			return false;
 	}
 
+	if (cpuidle_fast_idle())
+		return false;
+
 	return true;
 }
 
-- 
2.7.4