linux-kernel - Re: [PATCH] PM / devfreq: Remove redundant frequency adjustment from governors

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Date:   Thu, 17 May 2018 10:44:08 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Matthias Kaehlcke <mka@...omium.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] PM / devfreq: Remove redundant frequency adjustment
 from governors

Hi,

On 2018년 05월 17일 06:10, Matthias Kaehlcke wrote:
> The performance, powersave, simpleondemand and userspace governors
> determine a target frequency and then adjust it according to the
> df->min/max_freq limits that might have been set by user space. This
> adjustment is redundant, it is done in update_devfreq() for any
> governor, right after governor->get_target_freq().
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
>  drivers/devfreq/governor_performance.c    | 10 ++--------
>  drivers/devfreq/governor_powersave.c      |  5 -----
>  drivers/devfreq/governor_simpleondemand.c |  7 +------
>  drivers/devfreq/governor_userspace.c      | 16 ++++------------
>  4 files changed, 7 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
> index 4d23ecfbd948..31ee30622c00 100644
> --- a/drivers/devfreq/governor_performance.c
> +++ b/drivers/devfreq/governor_performance.c
> @@ -16,14 +16,8 @@
>  static int devfreq_performance_func(struct devfreq *df,
>  				    unsigned long *freq)
>  {
> -	/*
> -	 * target callback should be able to get floor value as
> -	 * said in devfreq.h
> -	 */
> -	if (!df->max_freq)
> -		*freq = UINT_MAX;
> -	else
> -		*freq = df->max_freq;
> +	*freq = UINT_MAX;
> +

It is difficult to understand why use UINT_MAX instead of df->max_freq.

Instead, after merged the commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq
when adding the devfreq device"), df->max/min_freq have the specific frequency
value always. So, we can change it as following without UINT_MAX. 

	*freq = df->max_freq;


>  	return 0;
>  }
>  
> diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
> index 0c42f23249ef..50a891f7c92d 100644
> --- a/drivers/devfreq/governor_powersave.c
> +++ b/drivers/devfreq/governor_powersave.c
> @@ -16,11 +16,6 @@
>  static int devfreq_powersave_func(struct devfreq *df,
>  				  unsigned long *freq)
>  {
> -	/*
> -	 * target callback should be able to get ceiling value as
> -	 * said in devfreq.h
> -	 */
> -	*freq = df->min_freq;
>  	return 0;

Each function have to keep their own function role.
Please keep '*freq = df->min_freq'.

>  }
>  
> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
> index 28e0f2de7100..7ed733c528f4 100644
> --- a/drivers/devfreq/governor_simpleondemand.c
> +++ b/drivers/devfreq/governor_simpleondemand.c
> @@ -27,7 +27,7 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>  	unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
>  	unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
>  	struct devfreq_simple_ondemand_data *data = df->data;
> -	unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;
> +	unsigned long max = UINT_MAX;

Use df->max_freq instead of UINT_MAX as following.

	unsigned long max = df->max_freq;

>  
>  	err = devfreq_update_stats(df);
>  	if (err)
> @@ -85,11 +85,6 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>  	b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
>  	*freq = (unsigned long) b;
>  
> -	if (df->min_freq && *freq < df->min_freq)
> -		*freq = df->min_freq;
> -	if (df->max_freq && *freq > df->max_freq)
> -		*freq = df->max_freq;
> -
>  	return 0;
>  }
>  
> diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
> index 080607c3f34d..378d84c011df 100644
> --- a/drivers/devfreq/governor_userspace.c
> +++ b/drivers/devfreq/governor_userspace.c
> @@ -26,19 +26,11 @@ static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
>  {
>  	struct userspace_data *data = df->data;
>  
> -	if (data->valid) {
> -		unsigned long adjusted_freq = data->user_frequency;
> -
> -		if (df->max_freq && adjusted_freq > df->max_freq)
> -			adjusted_freq = df->max_freq;
> -
> -		if (df->min_freq && adjusted_freq < df->min_freq)
> -			adjusted_freq = df->min_freq;
> -
> -		*freq = adjusted_freq;
> -	} else {
> +	if (data->valid)
> +		*freq = data->user_frequency;
> +	else
>  		*freq = df->previous_freq; /* No user freq specified yet */
> -	}
> +
>  	return 0;
>  }
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics