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Subject: Re: [PATCH V2 RESEND 3/4] PM / devfreq: bail out early if no freq
 changes in devfreq_set_target
To:     Dong Aisheng <aisheng.dong@nxp.com>, linux-pm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Cc:     dongas86@gmail.com, kernel@pengutronix.de, shawnguo@kernel.org,
        linux-imx@nxp.com, linux-kernel@vger.kernel.org,
        myungjoo.ham@samsung.com, kyungmin.park@samsung.com,
        cw00.choi@samsung.com, abel.vesa@nxp.com
References: <1616484011-26702-1-git-send-email-aisheng.dong@nxp.com>
 <1616484011-26702-4-git-send-email-aisheng.dong@nxp.com>
From:   Chanwoo Choi <cwchoi00@gmail.com>
Message-ID: <3054611c-4f43-8432-bd14-1733ab82804b@gmail.com>
Date:   Wed, 24 Mar 2021 00:01:52 +0900
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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@nxp.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