From: Len Brown <len.br...@intel.com>
While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
cpuidle to shallow idle states, there is no simple mechanism
to give the hardware permission to enter the deeptest state permitted by PM_QOS.
Here we create the "cpuidle.use_deepest" modparam to provide this capability.
"cpuidle.use_deepest=Y" can be set at boot-time, and
/sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
n.b.
Within the constraints of PM_QOS, this mechanism gives the hardware
permission to choose the deeptest power savings and highest latency
state available. And so choice will depend on the particular hardware.
Also, if PM_QOS is not informed of latency constraints, it can't help.
In that case, using this mechanism may result in entering high-latency
states that impact performance.
Signed-off-by: Len Brown <len.br...@intel.com>
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
drivers/cpuidle/cpuidle.c | 19 ++++++++++++++++
include/linux/cpuidle.h | 7 ++++++
kernel/sched/idle.c | 30 +++++++++++++++++++------
4 files changed, 53 insertions(+), 7 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 05496622b4ef..20f70de688bf 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -659,6 +659,10 @@
cpuidle.off=1 [CPU_IDLE]
disable the cpuidle sub-system
+ cpuidle.use_deepest=Y [CPU_IDLE]
+ Ignore cpuidle governor, always choose deepest
+ PM_QOS-legal CPU idle power saving state.
+
cpufreq.off=1 [CPU_FREQ]
disable the cpufreq sub-system
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 484cc8909d5c..afee5aab7719 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -34,6 +34,7 @@ LIST_HEAD(cpuidle_detected_devices);
static int enabled_devices;
static int off __read_mostly;
+static bool use_deepest __read_mostly;
static int initialized __read_mostly;
int cpuidle_disabled(void)
@@ -116,6 +117,10 @@ void cpuidle_use_deepest_state(bool enable)
preempt_enable();
}
+bool cpuidle_using_deepest_state(void)
+{
+ return use_deepest;
+}
/**
* cpuidle_find_deepest_state - Find the deepest available idle state.
* @drv: cpuidle driver for the given CPU.
@@ -127,6 +132,19 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
return find_deepest_state(drv, dev, UINT_MAX, 0, false);
}
+/**
+ * cpuidle_find_deepest_state_qos - Find the deepest available idle state.
+ * @drv: cpuidle driver for the given CPU.
+ * @dev: cpuidle device for the given CPU.
+ * Honors PM_QOS
+ */
+int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev)
+{
+ return find_deepest_state(drv, dev,
+ pm_qos_request(PM_QOS_CPU_DMA_LATENCY), 0, false);
+}
+
#ifdef CONFIG_SUSPEND
static void enter_s2idle_proper(struct cpuidle_driver *drv,
struct cpuidle_device *dev, int index)
@@ -681,4 +699,5 @@ static int __init cpuidle_init(void)
}
module_param(off, int, 0444);
+module_param(use_deepest, bool, 0644);
core_initcall(cpuidle_init);
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 8f7788d23b57..e3c2c9d1898f 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -198,19 +198,26 @@ static inline struct cpuidle_device
*cpuidle_get_device(void) {return NULL; }
#ifdef CONFIG_CPU_IDLE
extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
struct cpuidle_device *dev);
+extern int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev);
extern int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
struct cpuidle_device *dev);
extern void cpuidle_use_deepest_state(bool enable);
+extern bool cpuidle_using_deepest_state(void);
#else
static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{return -ENODEV; }
+static inline int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev)
+{return -ENODEV; }
static inline int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{return -ENODEV; }
static inline void cpuidle_use_deepest_state(bool enable)
{
}
+static inline bool cpuidle_using_deepest_state(void) {return false; }
#endif
/* kernel/sched/idle.c */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 257f4f0b4532..6c7348ae28ec 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -167,17 +167,33 @@ static void cpuidle_idle_call(void)
* until a proper wakeup interrupt happens.
*/
- if (idle_should_enter_s2idle() || dev->use_deepest_state) {
- if (idle_should_enter_s2idle()) {
- entered_state = cpuidle_enter_s2idle(drv, dev);
- if (entered_state > 0) {
- local_irq_enable();
- goto exit_idle;
- }
+ if (idle_should_enter_s2idle()) {
+ entered_state = cpuidle_enter_s2idle(drv, dev);
+ if (entered_state > 0) {
+ local_irq_enable();
+ goto exit_idle;
}
+ }
+ /*
+ * cpuidle_dev->user_deepest_state is per-device, and thus per-CPU.
+ * it is used to force power-savings, and thus does not obey PM_QOS.
+ */
+
+ if (dev->use_deepest_state) {
next_state = cpuidle_find_deepest_state(drv, dev);
call_cpuidle(drv, dev, next_state);
+ }
+
+ /*
+ * cpuidle_using_deepest_state() is system-wide, applying to all CPUs.
+ * When activated, Linux gives the hardware permission to go as deep
+ * as PM_QOS allows.
+ */
+
+ else if (cpuidle_using_deepest_state()) {
+ next_state = cpuidle_find_deepest_state_qos(drv, dev);
+ call_cpuidle(drv, dev, next_state);
} else {
/*
* Ask the cpuidle framework to choose a convenient idle state.
--
2.14.0-rc0
