linux-kernel - Re: [PATCH V2 RESEND 3/4] PM / devfreq: bail out early if no freq changes in devfreq_set

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Date:   Wed, 24 Mar 2021 00:01:52 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Dong Aisheng <aisheng.dong@....com>, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     dongas86@...il.com, kernel@...gutronix.de, shawnguo@...nel.org,
        linux-imx@....com, linux-kernel@...r.kernel.org,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        cw00.choi@...sung.com, abel.vesa@....com
Subject: Re: [PATCH V2 RESEND 3/4] PM / devfreq: bail out early if no freq
 changes in devfreq_set_target

On 21. 3. 23. 오후 4:20, Dong Aisheng wrote:
> It's unnecessary to set the same freq again and run notifier calls.
> 
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> ---
>   drivers/devfreq/devfreq.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 85927bd7ee76..a6ee91dd17bd 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -352,13 +352,16 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
>   {
>   	struct devfreq_freqs freqs;
>   	unsigned long cur_freq;
> -	int err = 0;
> +	int err;
>   
>   	if (devfreq->profile->get_cur_freq)
>   		devfreq->profile->get_cur_freq(devfreq->dev.parent, &cur_freq);
>   	else
>   		cur_freq = devfreq->previous_freq;
>   
> +	if (new_freq == cur_freq)
> +		return 0;

cur_freq is one of the OPP frequencies. But, new_freq is calculated from
governor algorithm. It means that new_freq is not one of the
frequencies. Actually, it is not efficient.

After devfreq->profile->target() which almost uses
devfreq_recommended_opp(), new_freq is one of OPP frequencies.

> +
>   	freqs.old = cur_freq;
>   	freqs.new = new_freq;
>   	devfreq_notify_transition(devfreq, &freqs, DEVFREQ_PRECHANGE);
> @@ -375,7 +378,7 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
>   	 * and DEVFREQ_POSTCHANGE because for showing the correct frequency
>   	 * change order of between devfreq device and passive devfreq device.
>   	 */
> -	if (trace_devfreq_frequency_enabled() && new_freq != cur_freq)
> +	if (trace_devfreq_frequency_enabled())
>   		trace_devfreq_frequency(devfreq, new_freq, cur_freq);
>   
>   	freqs.new = new_freq;
> @@ -390,7 +393,7 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
>   	if (devfreq->suspend_freq)
>   		devfreq->resume_freq = new_freq;
>   
> -	return err;
> +	return 0;
>   }
>   
>   /**
> 


-- 
Best Regards,
Samsung Electronics
Chanwoo Choi