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

Aubrey Li
2017-09-30T07:22:46Z

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@linux.intel.com>
---
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