diff mbox series

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

Message ID 12464461.O9o76ZdvQC@rjwysocki.net
State New
Headers show
Series [v1] thermal: gov_step_wise: Go straight to instance->lower when mitigation is over | expand

Commit Message

Rafael J. Wysocki June 22, 2024, 12:26 p.m. UTC 
From: Rafael J. Wysocki <rafael.j.wysocki@intel.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@oldschoolsolutions.biz>
Tested-by: Jens Glathe <jens.glathe@oldschoolsolutions.biz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/thermal/gov_step_wise.c |   23 +++++------------------
 1 file changed, 5 insertions(+), 18 deletions(-)

Comments

Rafael J. Wysocki June 25, 2024, 12:33 p.m. UTC | #1 
On Tue, Jun 25, 2024 at 9:34 AM Johan Hovold <johan@kernel.org> wrote:
>
> On Sat, Jun 22, 2024 at 02:26:33PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.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.
>
> typo: reverting

Thanks!

> > 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.
>
> Care to elaborate on what went wrong here? In my test of the previous
> fix I saw the frequency ramping up in steps as expected when the
> temperature dropped. Under what circumstances would that fail to happen?

System suspend-resume would interfere with that as it would call
thermal_zone_device_init().

> > 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.
>
> I've tested this patch on the Lenovo ThinkPad X13s, where I could
> reproduce the rc1 regression, and things works as intended with the
> fix applied to rc5:
>
> Tested-by: Johan Hovold <johan+linaro@kernel.org>
>
> The CPU frequency still oscillates heavily but now with a more
> sawtoothed curve.
>
> Not sure if it helps with performance, though, as running the CPU at
> full speed as soon as we drop below the threshold (with hysteresis)
> also means that we get back to running at the lowest frequency even
> faster.

True, but assuming that the reason for the mitigation is still there.
If it's actually gone, it's better to stop cooling as soon as it can
be done.

Thanks!
diff mbox series

Patch

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);