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SubjectRe: [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@linaro.org>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.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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