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

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Message-ID: <f8721601-3eb8-4655-a207-fb7e38de2867@piie.net>
Date: Tue, 13 Aug 2024 23:08:06 +0200
From: Peter Kästle <peter@...e.net>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 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: Re: [PATCH v1 4/4] thermal: gov_bang_bang: Use governor_data to
 reduce overhead

On 13.08.24 16:29, Rafael J. Wysocki wrote:
> 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>

Acked-by: Peter Kästle <peter@...e.net>

> ---
>   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 */
>   };
>   
>   /**
> 
> 
>