linux-kernel - Re: [PATCH] powercap/drivers/idle_inject: Specify idle state max latency

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Date:   Thu, 26 Mar 2020 20:14:34 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "open list:POWER MANAGEMENT CORE" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powercap/drivers/idle_inject: Specify idle state max latency

On Thu, Mar 26, 2020 at 3:48 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> Currently the idle injection framework uses the play_idle() function
> which puts the current CPU in an idle state. The idle state is the
> deepest one, as specified by the latency constraint when calling the
> subsequent play_idle_precise() function with the INT_MAX.
>
> The idle_injection is used by the cpuidle_cooling device which
> computes the idle / run duration to mitigate the temperature by
> injecting idle cycles. The cooling device has no control on the depth
> of the idle state.
>
> Allow finer control of the idle injection mechanism by allowing to
> specify the latency for the idle state. Thus the cooling device has
> the ability to have a guarantee on the exit latency of the idle states
> it is injecting.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/powercap/idle_inject.c | 27 ++++++++++++++++++++++++++-
>  include/linux/idle_inject.h    |  6 ++++++
>  2 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
> index cd1270614cc6..15e6f9b8023f 100644
> --- a/drivers/powercap/idle_inject.c
> +++ b/drivers/powercap/idle_inject.c
> @@ -61,12 +61,14 @@ struct idle_inject_thread {
>   * @timer: idle injection period timer
>   * @idle_duration_us: duration of CPU idle time to inject
>   * @run_duration_us: duration of CPU run time to allow
> + * @latency_us: max allowed latency
>   * @cpumask: mask of CPUs affected by idle injection
>   */
>  struct idle_inject_device {
>         struct hrtimer timer;
>         unsigned int idle_duration_us;
>         unsigned int run_duration_us;
> +       unsigned int latency_us;
>         unsigned long int cpumask[0];
>  };
>
> @@ -138,7 +140,8 @@ static void idle_inject_fn(unsigned int cpu)
>          */
>         iit->should_run = 0;
>
> -       play_idle(READ_ONCE(ii_dev->idle_duration_us));
> +       play_idle_precise(READ_ONCE(ii_dev->idle_duration_us) * NSEC_PER_USEC,
> +                         READ_ONCE(ii_dev->latency_us) * NSEC_PER_USEC);
>  }
>
>  /**
> @@ -169,6 +172,27 @@ void idle_inject_get_duration(struct idle_inject_device *ii_dev,
>         *idle_duration_us = READ_ONCE(ii_dev->idle_duration_us);
>  }
>
> +/**
> + * idle_inject_set_latency - set the maximum latency allowed
> + * @latency_us: set the latency requirement for the idle state
> + */
> +void idle_inject_set_latency(struct idle_inject_device *ii_dev,
> +                            unsigned int latency_us)
> +{
> +       WRITE_ONCE(ii_dev->latency_us, latency_us);
> +}
> +
> +/**
> + * idle_inject_get_latency - get the allowed latency
> + *
> + * Return: an unsigned int corresponding to the latency requirement
> + * for the idle state
> + */
> +unsigned int idle_inject_get_latency(struct idle_inject_device *ii_dev)
> +{
> +       return READ_ONCE(ii_dev->latency_us);
> +}
> +
>  /**
>   * idle_inject_start - start idle injections
>   * @ii_dev: idle injection control device structure
> @@ -297,6 +321,7 @@ struct idle_inject_device *idle_inject_register(struct cpumask *cpumask)
>         cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask);
>         hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>         ii_dev->timer.function = idle_inject_timer_fn;
> +       ii_dev->latency_us = UINT_MAX;
>
>         for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) {
>
> diff --git a/include/linux/idle_inject.h b/include/linux/idle_inject.h
> index a445cd1a36c5..b573fee589b9 100644
> --- a/include/linux/idle_inject.h
> +++ b/include/linux/idle_inject.h
> @@ -26,4 +26,10 @@ void idle_inject_set_duration(struct idle_inject_device *ii_dev,
>  void idle_inject_get_duration(struct idle_inject_device *ii_dev,
>                                  unsigned int *run_duration_us,
>                                  unsigned int *idle_duration_us);
> +
> +void idle_inject_set_latency(struct idle_inject_device *ii_dev,
> +                            unsigned int latency_ns);
> +
> +unsigned int idle_inject_get_latency(struct idle_inject_device *ii_dev);
> +
>  #endif /* __IDLE_INJECT_H__ */
> --

I would like to see a user of idle_inject_get_latency() before this goes in.