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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Sat, 25 Jun 2016 03:09:30 +0200
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Subject: Re: [RESEND PATCH v2 1/2] power/cpuidle: enhance the precision of
 state select
To: Zhaoyang Huang <zhaoyang.huang@linaro.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        zhaoyang.huang@spreadtrum.com, Thomas Gleixner <tglx@linutronix.de>
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On Fri, Jun 17, 2016 at 11:13 AM, Zhaoyang Huang
<zhaoyang.huang@linaro.org> wrote:
> In previous version, cpu_pm_enter is invoked

By whom?  Not by the core surely?

> after the governor select the state, which cause the executing time of cpu_pm_enter
> is included in the idle time. Moving it before the state selection.
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@spreadtrum.com>
> ---
>  kernel/sched/idle.c |   18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index bd12c6c..929da2e 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -5,6 +5,7 @@
>  #include <linux/cpu.h>
>  #include <linux/cpuidle.h>
>  #include <linux/cpuhotplug.h>
> +#include <linux/cpu_pm.h>
>  #include <linux/tick.h>
>  #include <linux/mm.h>
>  #include <linux/stackprotector.h>
> @@ -130,6 +131,7 @@ static void cpuidle_idle_call(void)
>         struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
>         struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
>         int next_state, entered_state;
> +       int ret;
>
>         /*
>          * Check if the idle task must be rescheduled. If it is the
> @@ -174,12 +176,16 @@ static void cpuidle_idle_call(void)
>                 /*
>                  * Ask the cpuidle framework to choose a convenient idle state.
>                  */
> -               next_state = cpuidle_select(drv, dev);
> -               entered_state = call_cpuidle(drv, dev, next_state);
> -               /*
> -                * Give the governor an opportunity to reflect on the outcome
> -                */
> -               cpuidle_reflect(dev, entered_state);
> +               ret = cpu_pm_enter();

"To move" usually means "take it away from there and put it here" as
far as kernel patches are concerned, but I only see it added here.

> +               if (!ret) {
> +                       next_state = cpuidle_select(drv, dev);
> +                       entered_state = call_cpuidle(drv, dev, next_state);
> +                       cpu_pm_exit();
> +                       /*
> +                        * Give the governor an opportunity to reflect on the outcome
> +                        */
> +                       cpuidle_reflect(dev, entered_state);
> +               }
>         }
>
>  exit_idle:
> --

No way I will agree to add that notification stuff to the core.

Thanks,
Rafael