linux-kernel - [PATCH v1 4/4] thermal: gov_bang_bang: Use governor

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Message-ID: <2285575.iZASKD2KPV@rjwysocki.net>
Date: Tue, 13 Aug 2024 16:29:11 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Peter Kästle <peter@...e.net>
Subject:
 [PATCH v1 4/4] thermal: gov_bang_bang: Use governor_data to reduce overhead

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

After running once, the for_each_trip_desc() loop in
bang_bang_manage() is pure needless overhead because it is not going to
make any changes unless a new cooling device has been bound to one of
the trips in the thermal zone or the system is resuming from sleep.

For this reason, make bang_bang_manage() set governor_data for the
thermal zone and check it upfront to decide whether or not it needs to
do anything.

However, governor_data needs to be reset in some cases to let
bang_bang_manage() know that it should walk the trips again, so add an
.update_tz() callback to the governor and make the core additionally
invoke it during system resume.

To avoid affecting the other users of that callback unnecessarily, add
a special notification reason for system resume, THERMAL_TZ_RESUME, and
also pass it to __thermal_zone_device_update() called during system
resume for consistency.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/thermal/gov_bang_bang.c |   18 ++++++++++++++++++
 drivers/thermal/thermal_core.c  |    3 ++-
 include/linux/thermal.h         |    1 +
 3 files changed, 21 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/thermal/gov_bang_bang.c
===================================================================
--- linux-pm.orig/drivers/thermal/gov_bang_bang.c
+++ linux-pm/drivers/thermal/gov_bang_bang.c
@@ -86,6 +86,10 @@ static void bang_bang_manage(struct ther
 	const struct thermal_trip_desc *td;
 	struct thermal_instance *instance;

+	/* If the code below has run already, nothing needs to be done. */
+	if (tz->governor_data)
+		return;
+
 	for_each_trip_desc(tz, td) {
 		const struct thermal_trip *trip = &td->trip;

@@ -107,11 +111,25 @@ static void bang_bang_manage(struct ther
 				bang_bang_set_instance_target(instance, 0);
 		}
 	}
+
+	tz->governor_data = (void *)true;
+}
+
+static void bang_bang_update_tz(struct thermal_zone_device *tz,
+				enum thermal_notify_event reason)
+{
+	/*
+	 * Let bang_bang_manage() know that it needs to walk trips after binding
+	 * a new cdev and after system resume.
+	 */
+	if (reason == THERMAL_TZ_BIND_CDEV || reason == THERMAL_TZ_RESUME)
+		tz->governor_data = NULL;
 }

 static struct thermal_governor thermal_gov_bang_bang = {
 	.name		= "bang_bang",
 	.trip_crossed	= bang_bang_control,
 	.manage		= bang_bang_manage,
+	.update_tz	= bang_bang_update_tz,
 };
 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.c
+++ linux-pm/drivers/thermal/thermal_core.c
@@ -1692,7 +1692,8 @@ static void thermal_zone_device_resume(s

 	thermal_debug_tz_resume(tz);
 	thermal_zone_device_init(tz);
-	__thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
+	thermal_governor_update_tz(tz, THERMAL_TZ_RESUME);
+	__thermal_zone_device_update(tz, THERMAL_TZ_RESUME);

 	complete(&tz->resume);
 	tz->resuming = false;
Index: linux-pm/include/linux/thermal.h
===================================================================
--- linux-pm.orig/include/linux/thermal.h
+++ linux-pm/include/linux/thermal.h
@@ -55,6 +55,7 @@ enum thermal_notify_event {
 	THERMAL_TZ_BIND_CDEV, /* Cooling dev is bind to the thermal zone */
 	THERMAL_TZ_UNBIND_CDEV, /* Cooling dev is unbind from the thermal zone */
 	THERMAL_INSTANCE_WEIGHT_CHANGED, /* Thermal instance weight changed */
+	THERMAL_TZ_RESUME, /* Thermal zone is resuming after system sleep */
 };

 /**