linux-kernel - Re: [PATCH v1] thermal: gov_step_wise: Go straight to instance->lower when mitigation is over

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Date: Mon, 24 Jun 2024 20:43:43 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, Lukasz Luba <lukasz.luba@....com>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Zhang Rui <rui.zhang@...el.com>, 
	Jens Glathe <jens.glathe@...schoolsolutions.biz>, Steev Klimaszewski <steev@...i.org>, 
	Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v1] thermal: gov_step_wise: Go straight to instance->lower
 when mitigation is over

On Sat, Jun 22, 2024 at 2:28 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Commit b6846826982b ("thermal: gov_step_wise: Restore passive polling
> management") attempted to fix a Step-Wise thermal governor issue
> introduced by commit 042a3d80f118 ("thermal: core: Move passive polling
> management to the core"), which caused the governor to leave cooling
> devices in high states, by partially revering that commit.
>
> However, this turns out to be insufficient on some systems due to
> interactions between the governor code restored by commit b6846826982b
> and the passive polling management in the thermal core.
>
> For this reason, revert commit b6846826982b and make the governor set
> the target cooling device state to the "lower" one as soon as the zone
> temperature falls below the threshold of the trip point corresponding
> to the given thermal instance, which means that thermal mitigation is
> not necessary any more.
>
> Before this change the "lower" cooling device state would be reached in
> steps through the passive polling mechanism which was questionable for
> three reasons: (1) cooling device were kept in high states when that was
> not necessary (and it could adversely impact performance), (2) it only
> worked for thermal zones with nonzero passive_delay_jiffies value, and
> (3) passive polling belongs to the core and should not be hijacked by
> governors for their internal purposes.
>
> Fixes: b6846826982b ("thermal: gov_step_wise: Restore passive polling management")
> Closes: https://lore.kernel.org/linux-pm/6759ce9f-281d-4fcd-bb4c-b784a1cc5f6e@oldschoolsolutions.biz
> Reported-by: Jens Glathe <jens.glathe@...schoolsolutions.biz>
> Tested-by: Jens Glathe <jens.glathe@...schoolsolutions.biz>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/thermal/gov_step_wise.c |   23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
>
> Index: linux-pm/drivers/thermal/gov_step_wise.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/gov_step_wise.c
> +++ linux-pm/drivers/thermal/gov_step_wise.c
> @@ -55,7 +55,11 @@ static unsigned long get_target_state(st
>                 if (cur_state <= instance->lower)
>                         return THERMAL_NO_TARGET;
>
> -               return clamp(cur_state - 1, instance->lower, instance->upper);
> +               /*
> +                * If 'throttle' is false, no mitigation is necessary, so
> +                * request the lower state for this instance.
> +                */
> +               return instance->lower;
>         }
>
>         return instance->target;
> @@ -93,23 +97,6 @@ static void thermal_zone_trip_update(str
>                 if (instance->initialized && old_target == instance->target)
>                         continue;
>
> -               if (trip->type == THERMAL_TRIP_PASSIVE) {
> -                       /*
> -                        * If the target state for this thermal instance
> -                        * changes from THERMAL_NO_TARGET to something else,
> -                        * ensure that the zone temperature will be updated
> -                        * (assuming enabled passive cooling) until it becomes
> -                        * THERMAL_NO_TARGET again, or the cooling device may
> -                        * not be reset to its initial state.
> -                        */
> -                       if (old_target == THERMAL_NO_TARGET &&
> -                           instance->target != THERMAL_NO_TARGET)
> -                               tz->passive++;
> -                       else if (old_target != THERMAL_NO_TARGET &&
> -                                instance->target == THERMAL_NO_TARGET)
> -                               tz->passive--;
> -               }
> -
>                 instance->initialized = true;
>
>                 mutex_lock(&instance->cdev->lock);
>

If there is no feedback, I'm going to assume that this is fine with everybody.

Thanks!