Re: [PATCH] cpuidle: enter_state: Don't needlessly calculate diff time

From: Rafael J. Wysocki
Date: Sun Sep 09 2018 - 15:40:45 EST


On Fri, Sep 7, 2018 at 8:55 PM Fieah Lim <kw@xxxxxxxxx> wrote:
>
> ktime_us_delta() is not that cheap on some platform,
> and I think this is also the right thing to do.
> While at it, fix some coding style as well.
>
> Signed-off-by: Fieah Lim <kw@xxxxxxxxx>

Fix your changelog at least to say that you optimize the code without
changing its functionality.

> ---
> drivers/cpuidle/cpuidle.c | 17 ++++++++---------
> 1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 6df894d65d9e..5f6b2c9b6555 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -247,21 +247,20 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
> if (!cpuidle_state_is_coupled(drv, index))
> local_irq_enable();
>
> - diff = ktime_us_delta(time_end, time_start);
> - if (diff > INT_MAX)
> - diff = INT_MAX;
> -
> - dev->last_residency = (int) diff;
> + dev->last_residency = 0;
>
> if (entered_state >= 0) {
> - /* Update cpuidle counters */
> - /* This can be moved to within driver enter routine
> + /* Update cpuidle counters
> + * This can be moved to within driver enter routine,
> * but that results in multiple copies of same code.
> */
> + diff = ktime_us_delta(time_end, time_start);
> + if (diff > INT_MAX)
> + diff = INT_MAX;
> +
> + dev->last_residency = (int)diff;
> dev->states_usage[entered_state].time += dev->last_residency;
> dev->states_usage[entered_state].usage++;
> - } else {
> - dev->last_residency = 0;
> }
>
> return entered_state;
> --
> 2.18.0
>