linux-kernel - Re: [PATCH 20/21] cpuidle: don't calculate time-diff if entered

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Message-ID: <524365FA.4090108@linaro.org>
Date:	Thu, 26 Sep 2013 00:38:50 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>, rjw@...k.pl
CC:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/21] cpuidle: don't calculate time-diff if entered_state
 == 0

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@...aro.org>
> ---
>  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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