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Message-ID: <2789916.f0jx01YxDY@kreacher>
Date: Fri, 08 Nov 2019 02:03:28 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: mathieu.poirier@...aro.org, mingo@...hat.com, peterz@...radead.org,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
ulf.hansson@...aro.org
Subject: Re: [PATCH V6 1/3] cpuidle: play_idle: Make play_idle more flexible
On Wednesday, October 30, 2019 8:51:39 AM CET Daniel Lezcano wrote:
> The play_idle function has two users, the intel powerclamp and the
> idle_injection.
>
> The idle injection cooling device uses the function via the
> idle_injection powercap's APIs. Unfortunately, play_idle is currently
> limited by the idle state depth: by default the deepest idle state is
> selected. On the ARM[64] platforms, most of the time it is the cluster
> idle state, the exit latency and the residency can be very high. That
> reduces the scope of the idle injection usage because the impact on
> the performances can be very significant.
>
> If the idle injection cycles can be done with a shallow state like a
> retention state, the cooling effect would eventually give similar
> results than the cpufreq cooling device.
>
> In order to prepare the function to receive an idle state parameter,
> let's replace the 'use_deepest_state' boolean field with 'use_state'
> and use this value to enter the specific idle state.
>
> The current code keeps the default behavior which is go to the deepest
> idle state.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> Acked-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
> V6:
> - Change use_state variable name by use_state_idx:
> https://lkml.org/lkml/2019/10/28/874
> V5:
> - Fix s2idle default idle state value:
> https://lkml.org/lkml/2019/10/15/522
> ---
> drivers/cpuidle/cpuidle.c | 21 +++++++++++----------
> include/linux/cpuidle.h | 13 ++++++-------
> kernel/sched/idle.c | 11 +++++++----
> 3 files changed, 24 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 0895b988fa92..18523ea6b11b 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -99,31 +99,31 @@ static int find_deepest_state(struct cpuidle_driver *drv,
> }
>
> /**
> - * cpuidle_use_deepest_state - Set/clear governor override flag.
> - * @enable: New value of the flag.
> + * cpuidle_use_state - Force the cpuidle framework to enter an idle state.
> + * @state: An integer for an idle state
> *
> - * Set/unset the current CPU to use the deepest idle state (override governors
> - * going forward if set).
> + * Specify an idle state the cpuidle framework must step in and bypass
> + * the idle state selection process.
> */
> -void cpuidle_use_deepest_state(bool enable)
> +void cpuidle_use_state(int index)
> {
> struct cpuidle_device *dev;
>
> preempt_disable();
> dev = cpuidle_get_device();
> if (dev)
> - dev->use_deepest_state = enable;
> + dev->use_state_idx = index;
> preempt_enable();
> }
>
> /**
> * cpuidle_find_deepest_state - Find the deepest available idle state.
> - * @drv: cpuidle driver for the given CPU.
> - * @dev: cpuidle device for the given CPU.
> */
> -int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> - struct cpuidle_device *dev)
> +int cpuidle_find_deepest_state(void)
> {
> + struct cpuidle_device *dev = cpuidle_get_device();
> + struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
This is totally wasteful for the cpuidle_idle_call() use case.
> +
> return find_deepest_state(drv, dev, UINT_MAX, 0, false);
> }
>
> @@ -554,6 +554,7 @@ static void __cpuidle_unregister_device(struct cpuidle_device *dev)
> static void __cpuidle_device_init(struct cpuidle_device *dev)
> {
> memset(dev->states_usage, 0, sizeof(dev->states_usage));
> + dev->use_state_idx = CPUIDLE_STATE_NOUSE;
> dev->last_residency = 0;
> dev->next_hrtimer = 0;
> }
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 4b6b5bea8f79..d53ad36cb2de 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -15,6 +15,7 @@
> #include <linux/list.h>
> #include <linux/hrtimer.h>
>
> +#define CPUIDLE_STATE_NOUSE -1
> #define CPUIDLE_STATE_MAX 10
> #define CPUIDLE_NAME_LEN 16
> #define CPUIDLE_DESC_LEN 32
> @@ -80,11 +81,11 @@ 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;
>
> + int use_state_idx;
> int last_state_idx;
> int last_residency;
> u64 poll_limit_ns;
> @@ -203,19 +204,17 @@ static inline struct cpuidle_device *cpuidle_get_device(void) {return NULL; }
> #endif
>
> #ifdef CONFIG_CPU_IDLE
> -extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> - struct cpuidle_device *dev);
> +extern int cpuidle_find_deepest_state(void);
> 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_state(int index);
> #else
> -static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> - struct cpuidle_device *dev)
> +static inline int cpuidle_find_deepest_state(void)
> {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 void cpuidle_use_state(int index)
> {
> }
> #endif
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 8dad5aa600ea..fb9fc93f1497 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -165,7 +165,8 @@ 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->use_state_idx != CPUIDLE_STATE_NOUSE) {
> if (idle_should_enter_s2idle()) {
> rcu_idle_enter();
>
> @@ -176,12 +177,14 @@ static void cpuidle_idle_call(void)
> }
>
> rcu_idle_exit();
> + next_state = cpuidle_find_deepest_state();
> + } else {
> + next_state = dev->use_state_idx;
> }
>
> tick_nohz_idle_stop_tick();
> rcu_idle_enter();
>
> - next_state = cpuidle_find_deepest_state(drv, dev);
> call_cpuidle(drv, dev, next_state);
> } else {
> bool stop_tick = true;
> @@ -328,7 +331,7 @@ void play_idle(unsigned long duration_us)
> rcu_sleep_check();
> preempt_disable();
> current->flags |= PF_IDLE;
> - cpuidle_use_deepest_state(true);
> + cpuidle_use_state(cpuidle_find_deepest_state());
And this assumes that the deepest state will not change for the whole
play_idle() duration, but what if it is disabled by user space in the
meantime?
>
> it.done = 0;
> hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> @@ -339,7 +342,7 @@ void play_idle(unsigned long duration_us)
> while (!READ_ONCE(it.done))
> do_idle();
>
> - cpuidle_use_deepest_state(false);
> + cpuidle_use_state(CPUIDLE_STATE_NOUSE);
> current->flags &= ~PF_IDLE;
>
> preempt_fold_need_resched();
>
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