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Date:   Wed, 14 Oct 2020 16:34:48 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, dri-devel@...ts.freedesktop.org
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        orjan.eide@....com, robh@...nel.org,
        alyssa.rosenzweig@...labora.com, steven.price@....com,
        airlied@...ux.ie, daniel@...ll.ch
Subject: Re: [PATCH 2/5] thermal: devfreq_cooling: get a copy of device status

On 21/09/2020 14:20, Lukasz Luba wrote:
> Devfreq cooling needs to now the correct status of the device in order
> to operate. Do not rely on Devfreq last_status which might be a stale data
> and get more up-to-date values of the load.
> 
> Devfreq framework can change the device status in the background. To
> mitigate this situation make a copy of the status structure and use it
> for internal calculations.
> 
> In addition this patch adds normalization function, which also makes sure
> that whatever data comes from the device, it is in a sane range.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  drivers/thermal/devfreq_cooling.c | 52 +++++++++++++++++++++++++------
>  1 file changed, 43 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/thermal/devfreq_cooling.c b/drivers/thermal/devfreq_cooling.c
> index 7063ccb7b86d..cf045bd4d16b 100644
> --- a/drivers/thermal/devfreq_cooling.c
> +++ b/drivers/thermal/devfreq_cooling.c
> @@ -227,6 +227,24 @@ static inline unsigned long get_total_power(struct devfreq_cooling_device *dfc,
>  							       voltage);
>  }
>  
> +static void _normalize_load(struct devfreq_dev_status *status)
> +{
> +	/* Make some space if needed */
> +	if (status->busy_time > 0xffff) {
> +		status->busy_time >>= 10;
> +		status->total_time >>= 10;
> +	}
> +
> +	if (status->busy_time > status->total_time)
> +		status->busy_time = status->total_time;
> +
> +	status->busy_time *= 100;
> +	status->busy_time /= status->total_time ? : 1;
> +
> +	/* Avoid division by 0 */
> +	status->busy_time = status->busy_time ? : 1;
> +	status->total_time = 100;
> +}

Not sure that works if the devfreq governor is not on-demand.

Is it possible to use the energy model directly in devfreq to compute
the energy consumption given the state transitions since the last reading ?

The power will be read directly from devfreq which will return:

nrj + (current_power * (jiffies - last_update)) / (jiffies - last_update)

The devfreq cooling device driver would result in a much simpler code, no?

>  static int devfreq_cooling_get_requested_power(struct thermal_cooling_device *cdev,
>  					       struct thermal_zone_device *tz,
> @@ -234,14 +252,22 @@ static int devfreq_cooling_get_requested_power(struct thermal_cooling_device *cd
>  {
>  	struct devfreq_cooling_device *dfc = cdev->devdata;
>  	struct devfreq *df = dfc->devfreq;
> -	struct devfreq_dev_status *status = &df->last_status;
> +	struct devfreq_dev_status status;
>  	unsigned long state;
> -	unsigned long freq = status->current_frequency;
> +	unsigned long freq;
>  	unsigned long voltage;
>  	u32 dyn_power = 0;
>  	u32 static_power = 0;
>  	int res;
>  
> +	mutex_lock(&df->lock);
> +	res = df->profile->get_dev_status(df->dev.parent, &status);
> +	mutex_unlock(&df->lock);
> +	if (res)
> +		return res;
> +
> +	freq = status.current_frequency;
> +
>  	state = freq_get_state(dfc, freq);
>  	if (state == THERMAL_CSTATE_INVALID) {
>  		res = -EAGAIN;
> @@ -269,16 +295,18 @@ static int devfreq_cooling_get_requested_power(struct thermal_cooling_device *cd
>  	} else {
>  		dyn_power = dfc->power_table[state];
>  
> +		_normalize_load(&status);
> +
>  		/* Scale dynamic power for utilization */
> -		dyn_power *= status->busy_time;
> -		dyn_power /= status->total_time;
> +		dyn_power *= status.busy_time;
> +		dyn_power /= status.total_time;
>  		/* Get static power */
>  		static_power = get_static_power(dfc, freq);
>  
>  		*power = dyn_power + static_power;
>  	}
>  
> -	trace_thermal_power_devfreq_get_power(cdev, status, freq, *power);
> +	trace_thermal_power_devfreq_get_power(cdev, &status, freq, *power);
>  
>  	return 0;
>  fail:
> @@ -312,14 +340,20 @@ static int devfreq_cooling_power2state(struct thermal_cooling_device *cdev,
>  {
>  	struct devfreq_cooling_device *dfc = cdev->devdata;
>  	struct devfreq *df = dfc->devfreq;
> -	struct devfreq_dev_status *status = &df->last_status;
> -	unsigned long freq = status->current_frequency;
> +	struct devfreq_dev_status status;
>  	unsigned long busy_time;
> +	unsigned long freq;
>  	s32 dyn_power;
>  	u32 static_power;
>  	s32 est_power;
>  	int i;
>  
> +	mutex_lock(&df->lock);
> +	status = df->last_status;
> +	mutex_unlock(&df->lock);
> +
> +	freq = status.current_frequency;
> +
>  	if (dfc->power_ops->get_real_power) {
>  		/* Scale for resource utilization */
>  		est_power = power * dfc->res_util;
> @@ -331,8 +365,8 @@ static int devfreq_cooling_power2state(struct thermal_cooling_device *cdev,
>  		dyn_power = dyn_power > 0 ? dyn_power : 0;
>  
>  		/* Scale dynamic power for utilization */
> -		busy_time = status->busy_time ?: 1;
> -		est_power = (dyn_power * status->total_time) / busy_time;
> +		busy_time = status.busy_time ?: 1;
> +		est_power = (dyn_power * status.total_time) / busy_time;
>  	}
>  
>  	/*
> 


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