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

Rafael J. Wysocki
2019-11-14T22:18:05Z

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();
> --