Message-ID: <3bbf1762-732b-4040-a3f1-eec575ee005e@arm.com>
Date: Thu, 24 Oct 2024 12:48:47 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v1 09/10] thermal: core: Use trip lists for trip crossing
 detection



On 10/16/24 12:35, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Modify the thermal core to use three lists of trip points:
> 
>   trips_high, containing trips with thresholds strictly above the current
>   thermal zone temperature,
> 
>   trips_reached, containing trips with thresholds at or below the current
>   zone temperature,
> 
>   trips_invalid, containing trips with temperature equal to
>   THERMAL_ZONE_INVALID,
> 
> where the first two lists are always sorted by the current trip
> threshold.
> 
> For each trip in trips_high, there is no mitigation under way and
> the trip threshold is equal to its temperature.  In turn, for each
> trip in trips_reached, there is mitigation under way and the trip
> threshold is equal to its low temperature.  The trips in trips_invalid,
> of course, need not be taken into consideration.
> 
> The idea is to make __thermal_zone_device_update() walk trips_high and
> trips_reached instead of walking the entire table of trip points in a
> thermal zone.  Usually, it will only need to walk a few entries in one
> of the lists and check one entry in the other list, depending on the
> direction of the zone temperature changes, because crossing many trips
> by the zone temperature in one go between two consecutive temperature
> checks should be unlikely (if it occurs often, the thermal zone
> temperature should probably be checked more often either or there
> are too many trips).
> 
> This also helps to eliminate one temporary trip list used for trip
> crossing notification (only one temporary list is needed for this
> purpose instead of two) and the remaining temporary list may be sorted
> by the current trip threshold value, like the trips_reached list, so
> the additional notify_temp field in struct thermal_trip_desc is not
> necessary any more.
> 
> Moreover, since the trips_reached and trips_high lists are sorted,
> the "low" and "high" values needed by thermal_zone_set_trips() can be
> determined in a straightforward way by looking at one end of each list.
> 
> Of course, additional work is needed in some places in order to
> maintain the ordering of the lists, but it is limited to situations
> that should be rare, like updating a trip point temperature or
> hysteresis, thermal zone initialization, or system resume.

Good point I agree. Even the trips from userspace that Daniel
proposed shouldn't impact that design decision IMHO.
Any disagreement (or am I missing something)?

> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>   drivers/thermal/thermal_core.c |  211 +++++++++++++++++++++++++----------------
>   drivers/thermal/thermal_core.h |    7 +
>   2 files changed, 136 insertions(+), 82 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_core.h
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.h
> +++ linux-pm/drivers/thermal/thermal_core.h
> @@ -33,7 +33,6 @@ struct thermal_trip_desc {
>   	struct thermal_trip_attrs trip_attrs;
>   	struct list_head list_node;
>   	struct list_head thermal_instances;
> -	int notify_temp;
>   	int threshold;
>   };
>   
> @@ -78,6 +77,9 @@ struct thermal_governor {
>    * @device:	&struct device for this thermal zone
>    * @removal:	removal completion
>    * @resume:	resume completion
> + * @trips_high:	trips above the current zone temperature
> + * @trips_reached:	trips below or at the current zone temperature
> + * @trips_invalid:	trips with invalid temperature
>    * @mode:		current mode of this thermal zone
>    * @devdata:	private pointer for device private data
>    * @num_trips:	number of trip points the thermal zone supports
> @@ -118,6 +120,9 @@ struct thermal_zone_device {
>   	struct completion removal;
>   	struct completion resume;
>   	struct attribute_group trips_attribute_group;
> +	struct list_head trips_high;
> +	struct list_head trips_reached;
> +	struct list_head trips_invalid;
>   	enum thermal_device_mode mode;
>   	void *devdata;
>   	int num_trips;
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -421,7 +421,7 @@ static void move_trip_to_sorted_list(str
>   
>   	/* Assume that the new entry is likely to be the last one. */
>   	list_for_each_entry_reverse(entry, list, list_node) {
> -		if (entry->notify_temp <= td->notify_temp) {
> +		if (entry->threshold <= td->threshold) {
>   			list_add(&td->list_node, &entry->list_node);
>   			return;
>   		}
> @@ -429,53 +429,6 @@ static void move_trip_to_sorted_list(str
>   	list_add(&td->list_node, list);
>   }
>   
> -static void handle_thermal_trip(struct thermal_zone_device *tz,
> -				struct thermal_trip_desc *td,
> -				struct list_head *way_up_list,
> -				struct list_head *way_down_list)
> -{
> -	const struct thermal_trip *trip = &td->trip;
> -	int old_threshold;
> -
> -	if (trip->temperature == THERMAL_TEMP_INVALID)
> -		return;
> -
> -	/*
> -	 * If the trip temperature or hysteresis has been updated recently,
> -	 * the threshold needs to be computed again using the new values.
> -	 * However, its initial value still reflects the old ones and that
> -	 * is what needs to be compared with the previous zone temperature
> -	 * to decide which action to take.
> -	 */
> -	old_threshold = td->threshold;
> -	td->threshold = trip->temperature;
> -
> -	if (tz->last_temperature >= old_threshold &&
> -	    tz->last_temperature != THERMAL_TEMP_INIT) {
> -		/*
> -		 * Mitigation is under way, so it needs to stop if the zone
> -		 * temperature falls below the low temperature of the trip.
> -		 * In that case, the trip temperature becomes the new threshold.
> -		 */
> -		if (tz->temperature < trip->temperature - trip->hysteresis) {
> -			td->notify_temp = trip->temperature - trip->hysteresis;
> -			move_trip_to_sorted_list(td, way_down_list);
> -		} else {
> -			td->threshold -= trip->hysteresis;
> -		}
> -	} else if (tz->temperature >= trip->temperature) {
> -		/*
> -		 * There is no mitigation under way, so it needs to be started
> -		 * if the zone temperature exceeds the trip one.  The new
> -		 * threshold is then set to the low temperature of the trip.
> -		 */
> -		td->notify_temp = trip->temperature;
> -		move_trip_to_sorted_list(td, way_up_list);
> -
> -		td->threshold -= trip->hysteresis;
> -	}
> -}
> -
>   static void thermal_zone_device_check(struct work_struct *work)
>   {
>   	struct thermal_zone_device *tz = container_of(work, struct
> @@ -484,9 +437,30 @@ static void thermal_zone_device_check(st
>   	thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
>   }
>   
> +static void move_to_trips_high(struct thermal_zone_device *tz,
> +			       struct thermal_trip_desc *td)
> +{
> +	td->threshold = td->trip.temperature;
> +	move_trip_to_sorted_list(td, &tz->trips_high);
> +}
> +
> +static void move_to_trips_reached(struct thermal_zone_device *tz,
> +				  struct thermal_trip_desc *td)
> +{
> +	td->threshold = td->trip.temperature - td->trip.hysteresis;
> +	move_trip_to_sorted_list(td, &tz->trips_reached);
> +}
> +
> +static void move_to_trips_invalid(struct thermal_zone_device *tz,
> +				  struct thermal_trip_desc *td)
> +{
> +	td->threshold = INT_MAX;
> +	list_move(&td->list_node, &tz->trips_invalid);
> +}
> +
>   static void thermal_zone_device_init(struct thermal_zone_device *tz)
>   {
> -	struct thermal_trip_desc *td;
> +	struct thermal_trip_desc *td, *next;
>   
>   	INIT_DELAYED_WORK(&tz->poll_queue, thermal_zone_device_check);
>   
> @@ -500,6 +474,21 @@ static void thermal_zone_device_init(str
>   		list_for_each_entry(instance, &td->thermal_instances, trip_node)
>   			instance->initialized = false;
>   	}
> +	/*
> +	 * At this point, all valid trips need to be moved to trips_high so that
> +	 * mitigation can be started if the zone temperature is above them.
> +	 */
> +	list_for_each_entry_safe(td, next, &tz->trips_invalid, list_node) {
> +		if (td->trip.temperature != THERMAL_TEMP_INVALID)
> +			move_to_trips_high(tz, td);
> +	}
> +	/* The trips_reached list may not be empty during system resume. */
> +	list_for_each_entry_safe(td, next, &tz->trips_reached, list_node) {
> +		if (td->trip.temperature == THERMAL_TEMP_INVALID)
> +			move_to_trips_invalid(tz, td);
> +		else
> +			move_to_trips_high(tz, td);
> +	}
>   }
>   
>   static void thermal_governor_trip_crossed(struct thermal_governor *governor,
> @@ -544,45 +533,120 @@ static void thermal_trip_crossed(struct
>   void thermal_zone_set_trip_hyst(struct thermal_zone_device *tz,
>   				struct thermal_trip *trip, int hyst)
>   {
> +	struct thermal_trip_desc *td = trip_to_trip_desc(trip);
> +
>   	WRITE_ONCE(trip->hysteresis, hyst);
>   	thermal_notify_tz_trip_change(tz, trip);
> +	/*
> +	 * If the zone temperature is above or at the trip tmperature, the trip
> +	 * is in the trips_reached list and its threshold is equal to its low
> +	 * temperature.  It needs to stay in that list, but its threshold needs
> +	 * to be updated and the list ordering may need to be restored.
> +	 */
> +	if (tz->temperature >= td->threshold)
> +		move_to_trips_reached(tz, td);
>   }
>   
>   void thermal_zone_set_trip_temp(struct thermal_zone_device *tz,
>   				struct thermal_trip *trip, int temp)
>   {
> -	if (trip->temperature == temp)
> +	struct thermal_trip_desc *td = trip_to_trip_desc(trip);
> +	int old_temp = trip->temperature;
> +
> +	if (old_temp == temp)
>   		return;
>   
>   	WRITE_ONCE(trip->temperature, temp);
>   	thermal_notify_tz_trip_change(tz, trip);
>   
> -	if (temp == THERMAL_TEMP_INVALID) {
> -		struct thermal_trip_desc *td = trip_to_trip_desc(trip);
> +	if (old_temp == THERMAL_TEMP_INVALID) {
> +		/*
> +		 * The trip was invalid before the change, so move it to the
> +		 * trips_high list regardless of the new temperature value
> +		 * because there is no mitigation under way for it.  If a
> +		 * mitigation needs to be started, the trip will be moved to the
> +		 * trips_reached list later.
> +		 */

Good comment

> +		move_to_trips_high(tz, td);
> +		return;
> +	}
>   
> +	if (temp == THERMAL_TEMP_INVALID) {
>   		/*
> -		 * If the trip has been crossed on the way up, some adjustments
> -		 * are needed to compensate for the lack of it going forward.
> +		 * If the trip is in the trips_reached list, mitigation is under
> +		 * way for it and it needs to be stopped because the trip is
> +		 * effectively going away.
>   		 */
>   		if (tz->temperature >= td->threshold)
>   			thermal_trip_crossed(tz, td, thermal_get_tz_governor(tz), false);
>   
> +		move_to_trips_invalid(tz, td);
> +		return;
> +	}
> +
> +	/*
> +	 * The trip stays on its current list, but its threshold needs to be
> +	 * updated due to the temperature change and the list ordering may need
> +	 * to be restored.
> +	 */
> +	if (tz->temperature >= td->threshold)
> +		move_to_trips_reached(tz, td);
> +	else
> +		move_to_trips_high(tz, td);
> +}
> +EXPORT_SYMBOL_GPL(thermal_zone_set_trip_temp);
> +
> +static void thermal_zone_handle_trips(struct thermal_zone_device *tz,
> +				      struct thermal_governor *governor,
> +				      int *low, int *high)
> +{
> +	struct thermal_trip_desc *td, *next;
> +	LIST_HEAD(way_down_list);
> +
> +	/* Check the trips that were below or at the zone temperature. */
> +	list_for_each_entry_safe_reverse(td, next, &tz->trips_reached, list_node) {
> +		if (td->threshold <= tz->temperature)
> +			break;
> +
> +		thermal_trip_crossed(tz, td, governor, false);
>   		/*
> -		 * Invalidate the threshold to avoid triggering a spurious
> -		 * trip crossing notification when the trip becomes valid.
> +		 * The current trips_high list needs to be processed before
> +		 * adding new entries to it, so put them on a temporary list.
>   		 */
> -		td->threshold = INT_MAX;
> +		list_move(&td->list_node, &way_down_list);
> +	}
> +	/* Check the trips that were previously above the zone temperature. */
> +	list_for_each_entry_safe(td, next, &tz->trips_high, list_node) {
> +		if (td->threshold > tz->temperature)
> +			break;
> +
> +		thermal_trip_crossed(tz, td, governor, true);
> +		move_to_trips_reached(tz, td);
> +	}

nit:
I would add and extra empty line here, since this is
quite separate from the loop above and has important
meaning.

> +	list_for_each_entry_safe(td, next, &way_down_list, list_node)
> +		move_to_trips_high(tz, td);
> +
> +	if (!list_empty(&tz->trips_reached)) {
> +		td = list_last_entry(&tz->trips_reached,
> +				     struct thermal_trip_desc, list_node);
> +		/*
> +		 * Set the "low" value below the current trip threshold in case
> +		 * the zone temperature is at that threshold and stays there,
> +		 * which would trigger a new interrupt immediately in vain.
> +		 */
> +		*low = td->threshold - 1;
> +	}
> +	if (!list_empty(&tz->trips_high)) {
> +		td = list_first_entry(&tz->trips_high,
> +				      struct thermal_trip_desc, list_node);
> +		*high = td->threshold;
>   	}
>   }
> -EXPORT_SYMBOL_GPL(thermal_zone_set_trip_temp);
>   
>   void __thermal_zone_device_update(struct thermal_zone_device *tz,
>   				  enum thermal_notify_event event)
>   {
>   	struct thermal_governor *governor = thermal_get_tz_governor(tz);
> -	struct thermal_trip_desc *td, *next;
> -	LIST_HEAD(way_down_list);
> -	LIST_HEAD(way_up_list);
>   	int low = -INT_MAX, high = INT_MAX;
>   	int temp, ret;
>   
> @@ -614,25 +678,7 @@ void __thermal_zone_device_update(struct
>   
>   	tz->notify_event = event;
>   
> -	for_each_trip_desc(tz, td) {
> -		handle_thermal_trip(tz, td, &way_up_list, &way_down_list);
> -
> -		if (td->threshold <= tz->temperature && td->threshold > low)
> -			low = td->threshold;
> -
> -		if (td->threshold >= tz->temperature && td->threshold < high)
> -			high = td->threshold;
> -	}
> -
> -	list_for_each_entry_safe(td, next, &way_up_list, list_node) {
> -		thermal_trip_crossed(tz, td, governor, true);
> -		list_del_init(&td->list_node);
> -	}
> -
> -	list_for_each_entry_safe_reverse(td, next, &way_down_list, list_node) {
> -		thermal_trip_crossed(tz, td, governor, false);
> -		list_del_init(&td->list_node);
> -	}
> +	thermal_zone_handle_trips(tz, governor, &low, &high);
>   
>   	thermal_thresholds_handle(tz, &low, &high);
>   
> @@ -1507,6 +1553,9 @@ thermal_zone_device_register_with_trips(
>   	}
>   
>   	INIT_LIST_HEAD(&tz->node);
> +	INIT_LIST_HEAD(&tz->trips_high);
> +	INIT_LIST_HEAD(&tz->trips_reached);
> +	INIT_LIST_HEAD(&tz->trips_invalid);
>   	ida_init(&tz->ida);
>   	mutex_init(&tz->lock);
>   	init_completion(&tz->removal);
> @@ -1536,7 +1585,7 @@ thermal_zone_device_register_with_trips(
>   		 * this only matters for the trips that start as invalid and
>   		 * become valid later.
>   		 */
> -		td->threshold = INT_MAX;
> +		move_to_trips_invalid(tz, td);
>   	}
>   
>   	tz->polling_delay_jiffies = msecs_to_jiffies(polling_delay);
> 
> 
> 

It took me a while to get the new code flow and idea.

Anyway, not that much controversial changes, which might
look like, on the first glance, LGTM.

Reviewed-by: Lukasz Luba <lukasz.luba@....com>

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