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

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(-)

-- 
2.17.1

On Thu, Nov 14, 2019 at 9:49 PM Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
>

> 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);


This is kind of artificial without the changes in the second patch, so
I would fold the [2/3] into this one.

Apart from that the patches look reasonable to me.

>

>         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();

> --