linux-kernel - Re: [PATCH V2] tick: Make sleep length calculation more accurate

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Message-ID: <524C1F75.307@linaro.org>
Date:	Wed, 02 Oct 2013 15:28:21 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	tglx@...utronix.de, sboyd@...eaurora.org
CC:	linux-kernel@...r.kernel.org, patches@...aro.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH V2] tick: Make sleep length calculation more accurate

On 10/02/2013 12:26 PM, Daniel Lezcano wrote:
> The sleep_length is computed in the tick_nohz_stop_sched_tick function but it
> is used later in the code with in between the local irq enabled.
>
> cpu_idle_loop
>    tick_nohz_idle_enter         [ exits with local irq enabled ]
>     __tick_nohz_idle_enter
>       tick_nohz_stop_sched_tick
>    ...
>
>    arch_cpu_idle
>       menu_select               [ uses here 'sleep_length' ]
>    ...
>
> Between the computation of the sleep length and its usage, some interrupts
> may occur, making the sleep length shorter than actually it is because of the
> interrupt processing, or different if the timer itself expired.
>
> This patch fixes that by moving the sleep_length computation in the
> tick_nohz_get_sleep_length function and using the tick device's next_event.
>
> As the sleep_length field is no longer needed, it is removed from the
> tick_sched structure.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>

Stephen,

I added your signed-off as the change in tick_nohz_get_sleep_length is 
the one you proposed previously.

   -- Daniel

> ---
>   include/linux/tick.h     |    2 --
>   kernel/time/tick-sched.c |    5 +++--
>   2 files changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index 5128d33..53dbbd7 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -48,7 +48,6 @@ enum tick_nohz_mode {
>    * @idle_exittime:	Time when the idle state was left
>    * @idle_sleeptime:	Sum of the time slept in idle with sched tick stopped
>    * @iowait_sleeptime:	Sum of the time slept in idle with sched tick stopped, with IO outstanding
> - * @sleep_length:	Duration of the current idle sleep
>    * @do_timer_lst:	CPU was the last one doing do_timer before going idle
>    */
>   struct tick_sched {
> @@ -67,7 +66,6 @@ struct tick_sched {
>   	ktime_t				idle_exittime;
>   	ktime_t				idle_sleeptime;
>   	ktime_t				iowait_sleeptime;
> -	ktime_t				sleep_length;
>   	unsigned long			last_jiffies;
>   	unsigned long			next_jiffies;
>   	ktime_t				idle_expires;
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 3612fc7..60b1dcd 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -673,7 +673,6 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
>   out:
>   	ts->next_jiffies = next_jiffies;
>   	ts->last_jiffies = last_jiffies;
> -	ts->sleep_length = ktime_sub(dev->next_event, now);
>
>   	return ret;
>   }
> @@ -837,8 +836,10 @@ void tick_nohz_irq_exit(void)
>   ktime_t tick_nohz_get_sleep_length(void)
>   {
>   	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
> +	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
> +	ktime_t now = ktime_get();
>
> -	return ts->sleep_length;
> +	return ktime_sub(dev->next_event, now);
>   }
>
>   static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
>


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