linux-kernel - Re: [PATCH] drivers: thermal: step_wise: add support for hysteresis

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Date:   Tue, 10 Dec 2019 12:21:17 +0530
From:   Amit Kucheria <amit.kucheria@...durent.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>, Keerthy <j-keerthy@...com>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amit.kucheria@...durent.com>
Cc:     Ram Chandrasekar <rkumbako@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] drivers: thermal: step_wise: add support for hysteresis

On Thu, Nov 21, 2019 at 11:21 AM Amit Kucheria <amit.kucheria@...aro.org> wrote:
>
> From: Ram Chandrasekar <rkumbako@...eaurora.org>
>
> 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@...eaurora.org>
> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
> [Rebased patch from downstream]
> Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>

Daniel, Rui: ping.

Keerthy: This works for you, right?

> ---
>  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;
>         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);
>
> @@ -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.
> +                */
> +               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);
> --
> 2.17.1
>