drivers: thermal: step_wise: add support for hysteresis
diff mbox

Message ID 20180507175408.2154-1-ilina@codeaurora.org
State Changes Requested
Delegated to: Zhang Rui
Headers show

Commit Message

Lina Iyer May 7, 2018, 5:54 p.m. UTC
From: Ram Chandrasekar <rkumbako@codeaurora.org>

From: Ram Chandrasekar <rkumbako@codeaurora.org>

Step wise governor increases the mitigation level when the temperature
goes above a threshold and will decrease the mitigation when the
temperature falls below the threshold. If it were a case, where the
temperature hovers around a threshold, the mitigation will be applied
and removed at every iteration. This reaction to the temperature is
inefficient for performance.

The use of hysteresis temperature could avoid this ping-pong of
mitigation by relaxing the mitigation to happen only when the
temperature goes below this lower hysteresis value.

Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
---
 drivers/thermal/step_wise.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

Comments

Daniel Lezcano May 8, 2018, 2:04 a.m. UTC | #1
On Mon, May 07, 2018 at 11:54:08AM -0600, Lina Iyer wrote:
> From: Ram Chandrasekar <rkumbako@codeaurora.org>
> 
> From: Ram Chandrasekar <rkumbako@codeaurora.org>
> 
> Step wise governor increases the mitigation level when the temperature
> goes above a threshold and will decrease the mitigation when the
> temperature falls below the threshold. If it were a case, where the
> temperature hovers around a threshold, the mitigation will be applied
> and removed at every iteration. This reaction to the temperature is
> inefficient for performance.
> 
> The use of hysteresis temperature could avoid this ping-pong of
> mitigation by relaxing the mitigation to happen only when the
> temperature goes below this lower hysteresis value.

I don't disagree with this but the ping-pong around a temperature is usually
avoided with a P-I-D computation which is implemented with the IPA governor.
Wouldn't be more interesting to add the power numbers like some other
platforms, so the IPA could be used?

You will probably have better results with the IPA than changing the step-wise
governor behavior (which may potentially impact other users).
Lina Iyer May 9, 2018, 4:25 p.m. UTC | #2
Hi Daniel,

On Tue, May 08 2018 at 20:04 -0600, Daniel Lezcano wrote:
>On Mon, May 07, 2018 at 11:54:08AM -0600, Lina Iyer wrote:
>> From: Ram Chandrasekar <rkumbako@codeaurora.org>
>>
>> From: Ram Chandrasekar <rkumbako@codeaurora.org>
>>
>> Step wise governor increases the mitigation level when the temperature
>> goes above a threshold and will decrease the mitigation when the
>> temperature falls below the threshold. If it were a case, where the
>> temperature hovers around a threshold, the mitigation will be applied
>> and removed at every iteration. This reaction to the temperature is
>> inefficient for performance.
>>
>> The use of hysteresis temperature could avoid this ping-pong of
>> mitigation by relaxing the mitigation to happen only when the
>> temperature goes below this lower hysteresis value.
>
>I don't disagree with this but the ping-pong around a temperature is usually
>avoided with a P-I-D computation which is implemented with the IPA governor.
>Wouldn't be more interesting to add the power numbers like some other
>platforms, so the IPA could be used?
>
Possibly. But we have had better thermal performance for our hardware, with
stepwise and custom governor. Much of the mitigation happens through the
firmware and hardware. The stepwise governor works well for us.

>You will probably have better results with the IPA than changing the step-wise
>governor behavior (which may potentially impact other users).
>
This should not impact others who have not implemented the
->get_trip_hyst method.

Thanks,
Lina
Zhang Rui July 26, 2018, 8:49 a.m. UTC | #3
Hi, Lina,

On 一, 2018-05-07 at 11:54 -0600, Lina Iyer wrote:
> From: Ram Chandrasekar <rkumbako@codeaurora.org>
> 
> From: Ram Chandrasekar <rkumbako@codeaurora.org>
> 
> Step wise governor increases the mitigation level when the
> temperature
> goes above a threshold and will decrease the mitigation when the
> temperature falls below the threshold. If it were a case, where the
> temperature hovers around a threshold, the mitigation will be applied
> and removed at every iteration. This reaction to the temperature is
> inefficient for performance.
> 
> The use of hysteresis temperature could avoid this ping-pong of
> mitigation by relaxing the mitigation to happen only when the
> temperature goes below this lower hysteresis value.
> 
the idea looks okay to me, just some minor comments.

> Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>
> Signed-off-by: Lina Iyer <ilina@codeaurora.org>
> ---
>  drivers/thermal/step_wise.c | 33 +++++++++++++++++++++++----------
>  1 file changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/thermal/step_wise.c
> b/drivers/thermal/step_wise.c
> index ee047ca43084..cf07e2269291 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -36,7 +36,7 @@
>   *       for this trip point
>   *    d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit
>   *       for this trip point
> - * If the temperature is lower than a trip point,
> + * If the temperature is lower than a hysteresis temperature,

1. if you update this, you should update "if the temperature is higher
than ..." as well.

2. the updated comment does not fully match the code change you made
below.

>   *    a. if the trend is THERMAL_TREND_RAISING, do nothing
>   *    b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
>   *       state for this trip point, if the cooling state already
> @@ -127,7 +127,7 @@ static void update_passive_instance(struct
> thermal_zone_device *tz,
>  
>  static void thermal_zone_trip_update(struct thermal_zone_device *tz,
> int trip)
>  {
> -	int trip_temp;
> +	int trip_temp, hyst_temp;
>  	enum thermal_trip_type trip_type;
>  	enum thermal_trend trend;
>  	struct thermal_instance *instance;
> @@ -135,22 +135,23 @@ static void thermal_zone_trip_update(struct
> thermal_zone_device *tz, int trip)
>  	int old_target;
>  
>  	if (trip == THERMAL_TRIPS_NONE) {
> -		trip_temp = tz->forced_passive;
> +		hyst_temp = trip_temp = tz->forced_passive;
>  		trip_type = THERMAL_TRIPS_NONE;
>  	} else {
>  		tz->ops->get_trip_temp(tz, trip, &trip_temp);
> +		hyst_temp = trip_temp;
> +		if (tz->ops->get_trip_hyst) {
> +			tz->ops->get_trip_hyst(tz, trip,
> &hyst_temp);
> +			hyst_temp = trip_temp - hyst_temp;
> +		}
>  		tz->ops->get_trip_type(tz, trip, &trip_type);
>  	}
>  
>  	trend = get_tz_trend(tz, trip);
>  
> -	if (tz->temperature >= trip_temp) {
> -		throttle = true;
> -		trace_thermal_zone_trip(tz, trip, trip_type);
> -	}
> -
> -	dev_dbg(&tz->device,
> "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
> -				trip, trip_type, trip_temp, trend,
> throttle);
> +	dev_dbg(&tz->device,
> +		"Trip%d[type=%d,temp=%d,hyst=%d]:trend=%d,throttle=%
> d\n",
> +		trip, trip_type, trip_temp, hyst_temp, trend,
> throttle);
>  
throttle is not set properly here, so this debug message does not make
sense.

thanks,
rui
>  	mutex_lock(&tz->lock);
>  
> @@ -159,6 +160,18 @@ static void thermal_zone_trip_update(struct
> thermal_zone_device *tz, int trip)
>  			continue;
>  
>  		old_target = instance->target;
> +		throttle = false;
> +		/*
> +		 * Lower the mitigation only if the temperature
> +		 * goes below the hysteresis temperature.
> +		 */
> +		if (tz->temperature >= trip_temp ||
> +		   (tz->temperature >= hyst_temp &&
> +		   old_target != THERMAL_NO_TARGET)) {
> +			throttle = true;
> +			trace_thermal_zone_trip(tz, trip,
> trip_type);
> +		}
> +

>  		instance->target = get_target_state(instance, trend,
> throttle);
>  		dev_dbg(&instance->cdev->device, "old_target=%d,
> target=%d\n",
>  					old_target, (int)instance-
> >target);

Patch
diff mbox

diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
index ee047ca43084..cf07e2269291 100644
--- a/drivers/thermal/step_wise.c
+++ b/drivers/thermal/step_wise.c
@@ -36,7 +36,7 @@ 
  *       for this trip point
  *    d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit
  *       for this trip point
- * If the temperature is lower than a trip point,
+ * If the temperature is lower than a hysteresis temperature,
  *    a. if the trend is THERMAL_TREND_RAISING, do nothing
  *    b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
  *       state for this trip point, if the cooling state already
@@ -127,7 +127,7 @@  static void update_passive_instance(struct thermal_zone_device *tz,
 
 static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 {
-	int trip_temp;
+	int trip_temp, hyst_temp;
 	enum thermal_trip_type trip_type;
 	enum thermal_trend trend;
 	struct thermal_instance *instance;
@@ -135,22 +135,23 @@  static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 	int old_target;
 
 	if (trip == THERMAL_TRIPS_NONE) {
-		trip_temp = tz->forced_passive;
+		hyst_temp = trip_temp = tz->forced_passive;
 		trip_type = THERMAL_TRIPS_NONE;
 	} else {
 		tz->ops->get_trip_temp(tz, trip, &trip_temp);
+		hyst_temp = trip_temp;
+		if (tz->ops->get_trip_hyst) {
+			tz->ops->get_trip_hyst(tz, trip, &hyst_temp);
+			hyst_temp = trip_temp - hyst_temp;
+		}
 		tz->ops->get_trip_type(tz, trip, &trip_type);
 	}
 
 	trend = get_tz_trend(tz, trip);
 
-	if (tz->temperature >= trip_temp) {
-		throttle = true;
-		trace_thermal_zone_trip(tz, trip, trip_type);
-	}
-
-	dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
-				trip, trip_type, trip_temp, trend, throttle);
+	dev_dbg(&tz->device,
+		"Trip%d[type=%d,temp=%d,hyst=%d]:trend=%d,throttle=%d\n",
+		trip, trip_type, trip_temp, hyst_temp, trend, throttle);
 
 	mutex_lock(&tz->lock);
 
@@ -159,6 +160,18 @@  static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 			continue;
 
 		old_target = instance->target;
+		throttle = false;
+		/*
+		 * Lower the mitigation only if the temperature
+		 * goes below the hysteresis temperature.
+		 */
+		if (tz->temperature >= trip_temp ||
+		   (tz->temperature >= hyst_temp &&
+		   old_target != THERMAL_NO_TARGET)) {
+			throttle = true;
+			trace_thermal_zone_trip(tz, trip, trip_type);
+		}
+
 		instance->target = get_target_state(instance, trend, throttle);
 		dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
 					old_target, (int)instance->target);