linux-kernel - Re: [PATCH 4/4] thermal: step_wise: Extend thermal step-wise governor to monitor falling temperature.

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Date:   Fri, 8 Nov 2019 12:54:15 -0700
From:   Ram Chandrasekar <rkumbako@...eaurora.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     rui.zhang@...el.com, edubezval@...il.com,
        daniel.lezcano@...aro.org, vincent.guittot@...aro.org,
        bjorn.andersson@...aro.org, robh+dt@...nel.org,
        amit.kucheria@...durent.com, mark.rutland@....com,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] thermal: step_wise: Extend thermal step-wise governor
 to monitor falling temperature.



On 9/18/2019 8:18 PM, Thara Gopinath wrote:
>>>From the step wise governor point of view, the policy decisions
> that has to taken on a thermal trip point that is defined to be monitored
> for falling temprature is the mirror opposite of the decisions it has
> to take on a trip point that is monitored for rising temperature.
> 
> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
> ---
>   drivers/thermal/step_wise.c | 59 +++++++++++++++++++++++++++++++++------------
>   1 file changed, 44 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
> index 6e051cb..aa8e0a0 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -35,7 +35,8 @@
>    *       deactivate the thermal instance
>    */
>   static unsigned long get_target_state(struct thermal_instance *instance,
> -				enum thermal_trend trend, bool throttle)
> +				enum thermal_trend trend, bool throttle,
> +				enum thermal_trip_monitor_type type)
>   {
>   	struct thermal_cooling_device *cdev = instance->cdev;
>   	unsigned long cur_state;
> @@ -65,11 +66,21 @@ static unsigned long get_target_state(struct thermal_instance *instance,
>   
>   	switch (trend) {
>   	case THERMAL_TREND_RAISING:
> -		if (throttle) {
> -			next_target = cur_state < instance->upper ?
> -				    (cur_state + 1) : instance->upper;
> -			if (next_target < instance->lower)
> -				next_target = instance->lower;
> +		if (type == THERMAL_TRIP_MONITOR_FALLING) {
> +			if (cur_state <= instance->lower) {
> +				if (!throttle)
> +					next_target = THERMAL_NO_TARGET;
> +			} else {
> +				if (!throttle)
> +					next_target = cur_state - 1;
> +			}
> +		} else {
> +			if (throttle) {
> +				next_target = cur_state < instance->upper ?
> +					    (cur_state + 1) : instance->upper;
> +				if (next_target < instance->lower)
> +					next_target = instance->lower;
> +			}
>   		}
>   		break;
>   	case THERMAL_TREND_RAISE_FULL:
> @@ -77,14 +88,23 @@ static unsigned long get_target_state(struct thermal_instance *instance,
>   			next_target = instance->upper;
>   		break;
>   	case THERMAL_TREND_DROPPING:
> -		if (cur_state <= instance->lower) {
> -			if (!throttle)
> -				next_target = THERMAL_NO_TARGET;
> +		if (type == THERMAL_TRIP_MONITOR_FALLING) {
> +			if (throttle) {
> +				next_target = cur_state < instance->upper ?
> +					(cur_state + 1) : instance->upper;
> +				if (next_target < instance->lower)
> +					next_target = instance->lower;
> +			}
>   		} else {
> -			if (!throttle) {
> -				next_target = cur_state - 1;
> -				if (next_target > instance->upper)
> -					next_target = instance->upper;
> +			if (cur_state <= instance->lower) {
> +				if (!throttle)
> +					next_target = THERMAL_NO_TARGET;
> +			} else {
> +				if (!throttle) {
> +					next_target = cur_state - 1;
> +					if (next_target > instance->upper)
> +						next_target = instance->upper;
> +				}
>   			}
>   		}
>   		break;
> @@ -117,6 +137,8 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
>   {
>   	int trip_temp;
>   	enum thermal_trip_type trip_type;
> +	enum thermal_trip_monitor_type monitor_type =
> +					THERMAL_TRIP_MONITOR_RISING;
>   	enum thermal_trend trend;
>   	struct thermal_instance *instance;
>   	bool throttle = false;
> @@ -130,9 +152,15 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
>   		tz->ops->get_trip_type(tz, trip, &trip_type);
>   	}
>   
> +	if (tz->ops->get_trip_monitor_type)
> +		tz->ops->get_trip_monitor_type(tz, trip, &monitor_type);
> +
>   	trend = get_tz_trend(tz, trip);
>   
> -	if (tz->temperature >= trip_temp) {
> +	if (((monitor_type == THERMAL_TRIP_MONITOR_RISING) &&
> +	      (tz->temperature >= trip_temp)) ||
> +	      ((monitor_type == THERMAL_TRIP_MONITOR_FALLING) &&
> +	      (tz->temperature <= trip_temp))) {
Governors monitoring warming devices need to have support for 
hysteresis. Assume a case where the device is in idle when the 
temperature goes below threshold and we trigger a mitigation. Even a 
minimal workload or even the processing of the threshold by the governor 
could warm the device and put the temperature above the threshold and we 
will have to remove any mitigation. To avoid this ping-pong, its best to 
add a hysteresis support.
>   		throttle = true;
>   		trace_thermal_zone_trip(tz, trip, trip_type);
>   	}
> @@ -147,7 +175,8 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
>   			continue;
>   
>   		old_target = instance->target;
> -		instance->target = get_target_state(instance, trend, throttle);
> +		instance->target = get_target_state(instance, trend, throttle,
> +						    monitor_type);
>   		dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
>   					old_target, (int)instance->target);
>   
>