Re: [PATCH V2 1/2] cpuidle: Replace use_deepest_state flag by forced_idle_latency_limit_ns

[Rafael J. Wysocki]

On Saturday, November 16, 2019 2:16:12 PM CET Daniel Lezcano 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.
> 
> In addition add the play_idle_precise() function getting a nanosec
> base latency constraint as parameter. The play_idle() function becomes
> a wrapper passing an U64_MAX to play_idle_precise().
> 
> Suggested-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> ---
>  drivers/cpuidle/cpuidle.c | 10 +++++-----
>  include/linux/cpu.h       |  6 +++++-
>  include/linux/cpuidle.h   |  6 +++---
>  kernel/sched/idle.c       | 14 +++++++-------
>  4 files changed, 20 insertions(+), 16 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/cpu.h b/include/linux/cpu.h
> index d0633ebdaa9c..4c9694e209a5 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -179,7 +179,11 @@ void arch_cpu_idle_dead(void);
>  int cpu_report_state(int cpu);
>  int cpu_check_up_prepare(int cpu);
>  void cpu_set_state_online(int cpu);
> -void play_idle(unsigned long duration_us);
> +void play_idle_precise(u64 duration_ns, u64 latency_ns);
> +static inline void play_idle(unsigned long duration_us)
> +{
> +	play_idle_precise(duration_us * NSEC_PER_USEC, U64_MAX);
> +}
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  bool cpu_wait_death(unsigned int cpu, int seconds);
> 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..0a817e907192 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();
>  
> @@ -311,7 +311,7 @@ static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
>  	return HRTIMER_NORESTART;
>  }
>  
> -void play_idle(unsigned long duration_us)
> +void play_idle_precise(u64 duration_ns, u64 latency_ns)
>  {
>  	struct idle_timer it;
>  
> @@ -323,29 +323,29 @@ void play_idle(unsigned long duration_us)
>  	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
>  	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
>  	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
> -	WARN_ON_ONCE(!duration_us);
> +	WARN_ON_ONCE(!duration_ns);
>  
>  	rcu_sleep_check();
>  	preempt_disable();
>  	current->flags |= PF_IDLE;
> -	cpuidle_use_deepest_state(true);
> +	cpuidle_use_deepest_state(latency_ns);
>  
>  	it.done = 0;
>  	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>  	it.timer.function = idle_inject_timer_fn;
> -	hrtimer_start(&it.timer, ns_to_ktime(duration_us * NSEC_PER_USEC),
> +	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
>  		      HRTIMER_MODE_REL_PINNED);
>  
>  	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();
>  	preempt_enable();
>  }
> -EXPORT_SYMBOL_GPL(play_idle);
> +EXPORT_SYMBOL_GPL(play_idle_precise);
>  
>  void cpu_startup_entry(enum cpuhp_state state)
>  {
> 

Queued up for 5.5 along with the [2/2], but I have made quite a few changes
to the patches, so please double check the result in my bleeding-edge branch.

Thanks!