linux-kernel - Re: [PATCH V4] thermal/core/power_allocator: reset thermal governor when trip point is changed

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Date:   Tue, 20 Jun 2023 12:07:39 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Di Shen <di.shen@...soc.com>
Cc:     lukasz.luba@....com, daniel.lezcano@...aro.org, rafael@...nel.org,
        rui.zhang@...el.com, amitk@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, xuewen.yan@...soc.com,
        jeson.gao@...soc.com, zhanglyra@...il.com, orsonzhai@...il.com
Subject: Re: [PATCH V4] thermal/core/power_allocator: reset thermal governor
 when trip point is changed

On Tue, Jun 20, 2023 at 11:46 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Mon, Jun 19, 2023 at 8:36 AM Di Shen <di.shen@...soc.com> wrote:
> >
> > When the thermal trip point is changed, the governor should
> > be reset so that the policy algorithm be updated to adapt to the
> > new trip point.
> >
> > This patch adds an ops for thermal the governor structure to reset
> > the governor. The ops is called when the trip point is changed.
> > For power allocator, the parameters of pid controller and the states
> > of power cooling devices can be reset when the passive trip point
> > is changed.
> >
> > Signed-off-by: Di Shen <di.shen@...soc.com>
> >
> > ---
> > V4:
> > - Compared to V3, handle it in thermal core instead of in governor.
> >
> > - Add an ops to the governor structure, and call it when a trip
> >   point is changed.
> >
> > - Define reset ops for power allocator.
> >
> > V3:
> > - Add fix tag.
> >
> > V2:
> > - Compared to v1, do not revert.
> >
> > - Add a variable(last_switch_on_temp) in power_allocator_params
> >   to record the last switch_on_temp value.
> >
> > - Adds a function to renew the update flag and update the
> >   last_switch_on_temp when thermal trips are writable.
> >
> > V1:
> > - Revert commit 0952177f2a1f.
> > ---
> > ---
> >  drivers/thermal/gov_power_allocator.c | 21 +++++++++++++++++++++
> >  drivers/thermal/thermal_trip.c        |  6 ++++++
> >  include/linux/thermal.h               |  1 +
> >  3 files changed, 28 insertions(+)
> >
> > diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
> > index 8642f1096b91..41d155adc616 100644
> > --- a/drivers/thermal/gov_power_allocator.c
> > +++ b/drivers/thermal/gov_power_allocator.c
> > @@ -729,10 +729,31 @@ static int power_allocator_throttle(struct thermal_zone_device *tz, int trip_id)
> >         return allocate_power(tz, trip.temperature);
> >  }
> >
> > +static int power_allocator_reset(struct thermal_zone_device *tz, int trip_id)
> > +{
> > +       int ret = 0;
> > +       struct thermal_trip trip;
> > +       struct power_allocator_params *params = tz->governor_data;
> > +
> > +       ret = __thermal_zone_get_trip(tz, trip_id, &trip);
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* Only need reset for passive trips */
> > +       if (trip.type != THERMAL_TRIP_PASSIVE)
> > +               return -EINVAL;
> > +
> > +       reset_pid_controller(params);
> > +       allow_maximum_power(tz, true);
> > +
> > +       return ret;
> > +}
> > +
> >  static struct thermal_governor thermal_gov_power_allocator = {
> >         .name           = "power_allocator",
> >         .bind_to_tz     = power_allocator_bind,
> >         .unbind_from_tz = power_allocator_unbind,
> >         .throttle       = power_allocator_throttle,
> > +       .reset          = power_allocator_reset,
> >  };
> >  THERMAL_GOVERNOR_DECLARE(thermal_gov_power_allocator);
> > diff --git a/drivers/thermal/thermal_trip.c b/drivers/thermal/thermal_trip.c
> > index 907f3a4d7bc8..52eb768fada8 100644
> > --- a/drivers/thermal/thermal_trip.c
> > +++ b/drivers/thermal/thermal_trip.c
> > @@ -173,6 +173,12 @@ int thermal_zone_set_trip(struct thermal_zone_device *tz, int trip_id,
> >         if (tz->trips && (t.temperature != trip->temperature || t.hysteresis != trip->hysteresis))
> >                 tz->trips[trip_id] = *trip;
> >
> > +       if (t.temperature != trip->temperature && tz->governor && tz->governor->reset) {
> > +               ret = tz->governor->reset(tz, trip_id);
> > +               if (ret)
> > +                       pr_warn_once("Failed to reset thermal governor\n");
>
> I'm not really sure if it is useful to print this message here.
>
> First off, the governors may print more precise diagnostic messages if
> they care.
>
> Second, what is the sysadmin supposed to do in response to this message?

In addition to the above, trip point temperatures may be updated in
other places too, for instance in response to notifications from
platform firmware and IMV this new callback should be also used in
those cases.  However, in those cases multiple trip points may change
at a time and the critical/hot trip point temperatures may be updated
too AFAICS.