Date:   Tue, 20 Jun 2023 11:20:04 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     daniel.lezcano@...aro.org, rui.zhang@...el.com,
        Di Shen <di.shen@...soc.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

Hi Rafael,


On 6/20/23 11:07, Rafael J. Wysocki wrote:
> 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.

IIRC the critical/hot trip points are handled differently, not using the
governors. The governors' 'throttle' callback would be called only
after we pass the test of 'critical/hot' [1].

What Di is facing is in the issue under the bucket of
'handle_non_critical_trips()' when the governor just tries to
work on stale data - old trip temp.

For the 2nd case IIUC the code, we pass the 'trip.temperature'
and should be ready for what you said (modification of that value).
Furthermore, the critical/hot situation is handled w/o governor
assistance, so we should be safe:
tz->ops->critical(tz) or tz->ops->hot(tz) and not
tz->governor->throttle(tz, trip)

Would you agree Rafael?

Regards,
Lukasz

[1] 
https://elixir.bootlin.com/linux/v6.3/source/drivers/thermal/thermal_core.c#L370

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