Re: [PATCH 20/21] cpuidle: don't calculate time-diff if entered_state== 0

From: Daniel Lezcano
Date: Wed Sep 25 2013 - 18:38:58 EST


On 09/22/2013 03:21 AM, Viresh Kumar wrote:
> If entered_state == 0, we don't need to set dev->last_residency to 'diff' as we
> will be setting it to zero without using its new value.

I don't get it, can you elaborate. We can be a long time in this state
(eg. if the prediction is false).

> And so move calculation of diff also inside the "if" statement.
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> drivers/cpuidle/cpuidle.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index bf80236..cb81689 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -77,23 +77,22 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>
> struct cpuidle_state *target_state = &drv->states[index];
> ktime_t time_start, time_end;
> - s64 diff;
>
> time_start = ktime_get();
>
> entered_state = target_state->enter(dev, drv, index);
>
> - time_end = ktime_get();
> + if (entered_state >= 0) {
> + s64 diff;
>
> - local_irq_enable();
> + time_end = ktime_get();
> + diff = ktime_to_us(ktime_sub(time_end, time_start));
>
> - diff = ktime_to_us(ktime_sub(time_end, time_start));
> - if (diff > INT_MAX)
> - diff = INT_MAX;
> + if (diff > INT_MAX)
> + diff = INT_MAX;
>
> - dev->last_residency = (int) diff;
> + dev->last_residency = (int) diff;
>
> - if (entered_state >= 0) {
> /* Update cpuidle counters */
> /* This can be moved to within driver enter routine
> * but that results in multiple copies of same code.
> @@ -104,6 +103,8 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
> dev->last_residency = 0;
> }
>
> + local_irq_enable();
> +
> return entered_state;
> }
>
>


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