Hi Amit,
On 11/21/2019 12:50 AM, Amit Kucheria wrote:
> From: Ram Chandrasekar <rkumbako@xxxxxxxxxxxxxx>
>
> Currently, step wise governor increases the mitigation when the
> temperature goes above a threshold and decreases the mitigation when the
> temperature goes below the threshold. If there is a case where the
> temperature is wavering around the threshold, the mitigation will be
> applied and removed every iteration, which is not very efficient.
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> [Rebased patch from downstream]
> Signed-off-by: Amit Kucheria <amit.kucheria@xxxxxxxxxx>
> ---
> drivers/thermal/step_wise.c | 35 ++++++++++++++++++++++++-----------
> 1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
> index 6e051cbd824ff..2c8a34a7cf959 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -24,7 +24,7 @@
> * 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
> @@ -115,30 +115,31 @@ 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;
> - bool throttle = false;
> + bool throttle;
There is no need to remove throttle = false here. You are setting it to
false later down.
> 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 value is not final here. Why is the debug print and the setting
of throttle reversed ? Idea is to print the final value of
throttle.
>
> mutex_lock(&tz->lock);
>
> @@ -147,6 +148,18 @@ 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.
> + */
I think this requires more comment here on why there is a check for
old_target != THERMAL_NO_TARGET. Basically to ensure that the hysteresis
is considered only when temperature is dropping.
> + 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);
>
--
Warm Regards
Thara
