linux-kernel - Re: [PATCH v1 11/16] thermal: gov_fair_share: Use .manage() callback instead of .throttle()

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Message-ID: <370ff15c-fc44-4ba6-a357-f06e89d67250@arm.com>
Date: Fri, 19 Apr 2024 19:28:50 +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>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v1 11/16] thermal: gov_fair_share: Use .manage() callback
 instead of .throttle()



On 4/10/24 17:57, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The Fair Share governor tries very hard to be stateless and so it
> calls get_trip_level() from fair_share_throttle() every time, even
> though the number produced by this function for all of the trips
> during a given thermal zone update is actually the same.  Since
> get_trip_level() walks all of the trips in the thermal zone every
> time it is called, doing this may generate quite a bit of completely
> useless overhead.
> 
> For this reason, make the governor use the new .manage() callback
> instead of .throttle() which allows it to call get_trip_level() just
> once and use the value computed by it to handle all of the trips.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>   drivers/thermal/gov_fair_share.c |   37 ++++++++++++++++++++++++++-----------
>   1 file changed, 26 insertions(+), 11 deletions(-)
> 
> Index: linux-pm/drivers/thermal/gov_fair_share.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/gov_fair_share.c
> +++ linux-pm/drivers/thermal/gov_fair_share.c
> @@ -53,6 +53,7 @@ static long get_target_state(struct ther
>    * fair_share_throttle - throttles devices associated with the given zone
>    * @tz: thermal_zone_device
>    * @trip: trip point
> + * @trip_level: number of trips crossed by the zone temperature
>    *
>    * Throttling Logic: This uses three parameters to calculate the new
>    * throttle state of the cooling devices associated with the given zone.
> @@ -61,22 +62,19 @@ static long get_target_state(struct ther
>    * P1. max_state: Maximum throttle state exposed by the cooling device.
>    * P2. percentage[i]/100:
>    *	How 'effective' the 'i'th device is, in cooling the given zone.
> - * P3. cur_trip_level/max_no_of_trips:
> + * P3. trip_level/max_no_of_trips:
>    *	This describes the extent to which the devices should be throttled.
>    *	We do not want to throttle too much when we trip a lower temperature,
>    *	whereas the throttling is at full swing if we trip critical levels.
> - *	(Heavily assumes the trip points are in ascending order)
>    * new_state of cooling device = P3 * P2 * P1
>    */
> -static int fair_share_throttle(struct thermal_zone_device *tz,
> -			       const struct thermal_trip *trip)
> +static void fair_share_throttle(struct thermal_zone_device *tz,
> +				const struct thermal_trip *trip,
> +				int trip_level)
>   {
>   	struct thermal_instance *instance;
>   	int total_weight = 0;
>   	int total_instance = 0;
> -	int cur_trip_level = get_trip_level(tz);
> -
> -	lockdep_assert_held(&tz->lock);
>   
>   	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
>   		if (instance->trip != trip)
> @@ -99,18 +97,35 @@ static int fair_share_throttle(struct th
>   			percentage = (instance->weight * 100) / total_weight;
>   
>   		instance->target = get_target_state(tz, cdev, percentage,
> -						    cur_trip_level);
> +						    trip_level);
>   
>   		mutex_lock(&cdev->lock);
>   		__thermal_cdev_update(cdev);
>   		mutex_unlock(&cdev->lock);
>   	}
> +}
>   
> -	return 0;
> +static void fair_share_manage(struct thermal_zone_device *tz)
> +{
> +	int trip_level = get_trip_level(tz);
> +	const struct thermal_trip_desc *td;
> +
> +	lockdep_assert_held(&tz->lock);
> +
> +	for_each_trip_desc(tz, td) {
> +		const struct thermal_trip *trip = &td->trip;
> +
> +		if (trip->temperature == THERMAL_TEMP_INVALID ||
> +		    trip->type == THERMAL_TRIP_CRITICAL ||
> +		    trip->type == THERMAL_TRIP_HOT)
> +			continue;
> +
> +		fair_share_throttle(tz, trip, trip_level);
> +	}
>   }
>   
>   static struct thermal_governor thermal_gov_fair_share = {
> -	.name		= "fair_share",
> -	.throttle	= fair_share_throttle,
> +	.name	= "fair_share",
> +	.manage	= fair_share_manage,
>   };
>   THERMAL_GOVERNOR_DECLARE(thermal_gov_fair_share);
> 
> 
> 

LGTM

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