Re: [PATCH v1 4/4] thermal: gov_bang_bang: Use governor_data to reduce overhead

["Zhang, Rui" <rui.zhang@intel.com>]

On Tue, 2024-08-13 at 16:29 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.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@intel.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(instanc
> e, 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;
>  }

can we do the cdev initialization for BIND_CDEV and RESUME notification
in .update_tz() directly?

Then we don't need .manage() callback. This makes more sense to me
because bang_bang governor cares about trip point crossing only.

thanks,
rui
>  
>  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 */
>  };
>  
>  /**
> 
> 
>