[PATCH V1 1/3] cpuidle: Replace use_deepest_state flag by forced_idle_latency_limit_ns

Daniel Lezcano
2019-11-14T20:49:28Z

We want to specify a latency constraint when choosing an idle state at
play_idle time. Instead of duplicating the information in the
structure or propagate the latency in the call stack, change the
use_deepest_state by forced_latency_limit_ns to introduce this
constraint. The idea being that when it is set, idle is forced
(i.e. no governors), but there is a latency limit for the state to
use.

A zero latency constraint means "do not use the deepest idle state
path" as the 'use_deepest_state' boolean was used in the
cpuidle_idle_call.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
drivers/cpuidle/cpuidle.c | 10 +++++-----
include/linux/cpuidle.h | 6 +++---
kernel/sched/idle.c | 6 +++---
3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 44ae39f2b47a..62226fadc02d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -100,19 +100,19 @@ static int find_deepest_state(struct cpuidle_driver *drv,

/**
* cpuidle_use_deepest_state - Set/clear governor override flag.
- * @enable: New value of the flag.
+ * @latency_limit_ns: A latency limit constraint
*
- * Set/unset the current CPU to use the deepest idle state (override governors
- * going forward if set).
+ * Set/unset the current CPU to use the deepest idle state with the exit
+ * latency within @latency_limit_ns
*/
-void cpuidle_use_deepest_state(bool enable)
+void cpuidle_use_deepest_state(u64 latency_limit_ns)
{
struct cpuidle_device *dev;

preempt_disable();
dev = cpuidle_get_device();
if (dev)
- dev->use_deepest_state = enable;
+ dev->forced_idle_latency_limit_ns = latency_limit_ns;
preempt_enable();
}

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index d23a3b1ddcf6..1f3f4dd01e48 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -83,7 +83,6 @@ struct cpuidle_driver_kobj;
struct cpuidle_device {
unsigned int registered:1;
unsigned int enabled:1;
- unsigned int use_deepest_state:1;
unsigned int poll_time_limit:1;
unsigned int cpu;
ktime_t next_hrtimer;
@@ -91,6 +90,7 @@ struct cpuidle_device {
int last_state_idx;
int last_residency;
u64 poll_limit_ns;
+ u64 forced_idle_latency_limit_ns;
struct cpuidle_state_usage states_usage[CPUIDLE_STATE_MAX];
struct cpuidle_state_kobj *kobjs[CPUIDLE_STATE_MAX];
struct cpuidle_driver_kobj *kobj_driver;
@@ -210,7 +210,7 @@ extern int cpuidle_find_deepest_state(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 void cpuidle_use_deepest_state(u64 latency_limit_ns);
#else
static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
@@ -218,7 +218,7 @@ static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
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 void cpuidle_use_deepest_state(u64 latency_limit_ns)
{
}
#endif
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8dad5aa600ea..d4681b3d7074 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -165,7 +165,7 @@ 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() || dev->forced_idle_latency_limit_ns) {
if (idle_should_enter_s2idle()) {
rcu_idle_enter();

@@ -328,7 +328,7 @@ void play_idle(unsigned long duration_us)
rcu_sleep_check();
preempt_disable();
current->flags |= PF_IDLE;
- cpuidle_use_deepest_state(true);
+ cpuidle_use_deepest_state(1);

it.done = 0;
hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
@@ -339,7 +339,7 @@ void play_idle(unsigned long duration_us)
while (!READ_ONCE(it.done))
do_idle();

- cpuidle_use_deepest_state(false);
+ cpuidle_use_deepest_state(0);
current->flags &= ~PF_IDLE;

preempt_fold_need_resched();
--
2.17.1