Re: [PATCH v2 1/4] thermal: power_allocator: relax the requirement of a sustainable_power in tzp

Javi Merino
2015-08-11T17:37:20Z

On Tue, Aug 11, 2015 at 02:42:20PM +0100, Punit Agrawal wrote:
> Hi Javi,
>
> A few nitpicks and a comment below.
>
> Javi Merino <javi.merino@arm.com> writes:
>
> > The power allocator governor currently requires that a sustainable power
> > is passed as part of the thermal zone's thermal zone parameters. If
> > that parameter is not provided, it doesn't register with the thermal
> > zone.
> >
> > While this parameter is strongly recommended for optimal performance, it
> > doesn't need to be mandatory. Relax the requirement and allow the
> > governor to bind to thermal zones that don't provide it by estimating it
> > from the cooling devices' power model.
> >
> > Cc: Zhang Rui <rui.zhang@intel.com>
> > Cc: Eduardo Valentin <edubezval@gmail.com>
> > Signed-off-by: Javi Merino <javi.merino@arm.com>
> > ---
> > drivers/thermal/power_allocator.c | 62 +++++++++++++++++++++++++++++++++------
> > drivers/thermal/thermal_core.c | 28 ++++++++++++++++++
> > include/linux/thermal.h | 6 ++++
> > 3 files changed, 87 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/thermal/power_allocator.c b/drivers/thermal/power_allocator.c
> > index 63a448f9d93b..f78836c2da26 100644
> > --- a/drivers/thermal/power_allocator.c
> > +++ b/drivers/thermal/power_allocator.c
> > @@ -73,6 +73,39 @@ struct power_allocator_params {
> > };
> >
> > /**
> > + * estimate_sustainable_power() - Estimate the sustainable power of a thermal zone
> > + * @tz: thermal zone we are operating in
> > + *
> > + * For thermal zones that don't provide a sustainable_power in their
> > + * thermal_zone_params, estimate one. Calculate it using the minimum
> > + * power of all the cooling devices as that gives a valid value that
> > + * can give some degree of functionality. For optimal performance of
> > + * this governor, provide a sustainable_power in the thermal zone's
> > + * thermal_zone_params.
> > + */
> > +static u32 estimate_sustainable_power(struct thermal_zone_device *tz)
> > +{
> > + u32 sustainable_power = 0;
> > + struct thermal_instance *instance;
> > + struct power_allocator_params *params = tz->governor_data;
> > +
> > + list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> > + struct thermal_cooling_device *cdev = instance->cdev;
> > + u32 min_power;
> > +
> > + if (instance->trip != params->trip_max_desired_temperature)
> > + continue;
> > +
> > + if (power_actor_get_min_power(cdev, tz, &min_power))
> > + continue;
> > +
> > + sustainable_power += min_power;
> > + }
> > +
> > + return sustainable_power;
> > +}
> > +
> > +/**
> > * pid_controller() - PID controller
> > * @tz: thermal zone we are operating in
> > * @current_temp: the current temperature in millicelsius
> > @@ -98,6 +131,7 @@ static u32 pid_controller(struct thermal_zone_device *tz,
> > {
> > s64 p, i, d, power_range;
> > s32 err, max_power_frac;
> > + u32 sustainable_power;
> > struct power_allocator_params *params = tz->governor_data;
> >
> > max_power_frac = int_to_frac(max_allocatable_power);
> > @@ -138,8 +172,11 @@ static u32 pid_controller(struct thermal_zone_device *tz,
> >
> > power_range = p + i + d;
> >
> > + sustainable_power = tz->tzp->sustainable_power ?:
> > + estimate_sustainable_power(tz);
> > +
> > /* feed-forward the known sustainable dissipatable power */
> > - power_range = tz->tzp->sustainable_power + frac_to_int(power_range);
> > + power_range = sustainable_power + frac_to_int(power_range);
> >
> > power_range = clamp(power_range, (s64)0, (s64)max_allocatable_power);
> >
> > @@ -418,18 +455,18 @@ static int power_allocator_bind(struct thermal_zone_device *tz)
> > int ret;
> > struct power_allocator_params *params;
> > unsigned long switch_on_temp, control_temp;
> > - u32 temperature_threshold;
> > + u32 sustainable_power, temperature_threshold;
> >
> > - if (!tz->tzp || !tz->tzp->sustainable_power) {
> > - dev_err(&tz->device,
> > - "power_allocator: missing sustainable_power\n");
> > + if (!tz->tzp)
> > return -EINVAL;
> > - }
> >
> > params = devm_kzalloc(&tz->device, sizeof(*params), GFP_KERNEL);
> > if (!params)
> > return -ENOMEM;
> >
> > + if (!tz->tzp->sustainable_power)
> > + dev_warn(&tz->device, "power_allocator: sustainable_power will be estimated\n");
> > +
> > ret = get_governor_trips(tz, params);
> > if (ret) {
> > dev_err(&tz->device,
> > @@ -448,13 +485,20 @@ static int power_allocator_bind(struct thermal_zone_device *tz)
> > if (ret)
> > goto free;
> >
> > + /*
> > + * Provide an arbitrary sustainable_power to set the default
> > + * values of k_po and k_pu. We can estimate sustainable_power
> ^
> can not
> > + * at this point because no cooling devices have been
> > + * registered yet. By providing an arbitrary value we get
> > + * better defaults that setting k_po and k_pu to 0.
> ^
> than

Fixed both.

> > + */
> > + sustainable_power = tz->tzp->sustainable_power ?: 2500;
> > temperature_threshold = control_temp - switch_on_temp;
> >
> > tz->tzp->k_po = tz->tzp->k_po ?:
> > - int_to_frac(tz->tzp->sustainable_power) / temperature_threshold;
> > + int_to_frac(sustainable_power) / temperature_threshold;
> > tz->tzp->k_pu = tz->tzp->k_pu ?:
> > - int_to_frac(2 * tz->tzp->sustainable_power) /
> > - temperature_threshold;
> > + int_to_frac(2 * sustainable_power) / temperature_threshold;
>
> As we are being conservative with our estimation of sustainable power
> (sum of mins) when it is not explicitly specified, should we be
> conservative here and let the proportional terms, k_po and k_pu be zero
> as well?

Yes, we could do. If we set it to zero, all cooling devices will be
set to the maximum cooling state when the governor is active. If we
set it to a valid(ish) value, it will do a bit of thermal control.
It's not perfect but I think it's better to have a bad estimate than
no estimate.

> > tz->tzp->k_i = tz->tzp->k_i ?: int_to_frac(10) / 1000;
> > /*
> > * The default for k_d and integral_cutoff is 0, so we can
> > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > index 4ca211be4c0f..d26bc9e6f936 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -997,6 +997,34 @@ int power_actor_get_max_power(struct thermal_cooling_device *cdev,
> > }
> >
> > /**
> > + * power_actor_get_min_power() - get the mainimum power that a cdev can consume
> > + * @cdev: pointer to &thermal_cooling_device
> > + * @tz: a valid thermal zone device pointer
> > + * @min_power: pointer in which to store the minimum power
> > + *
> > + * Calculate the minimum power consumption in milliwats that the
> > + * cooling device can currently consume and store it in @min_power.
> > + *
> > + * Return: 0 on success, -EINVAL if @cdev doesn't support the
> > + * power_actor API or -E* on other error.
> > + */
> > +int power_actor_get_min_power(struct thermal_cooling_device *cdev,
> > + struct thermal_zone_device *tz, u32 *min_power)
> > +{
> > + unsigned long max_state;
> > + int ret;
> > +
> > + if (!cdev_is_power_actor(cdev))
> > + return -EINVAL;
> > +
> > + ret = cdev->ops->get_max_state(cdev, &max_state);
> > + if (ret)
> > + return ret;
> > +
> > + return cdev->ops->state2power(cdev, tz, max_state, min_power);
> > +}
> > +
> > +/**
> > * power_actor_set_power() - limit the maximum power that a cooling device can consume
> > * @cdev: pointer to &thermal_cooling_device
> > * @instance: thermal instance to update
> > diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> > index 037e9df2f610..f99d934d373a 100644
> > --- a/include/linux/thermal.h
> > +++ b/include/linux/thermal.h
> > @@ -384,6 +384,8 @@ static inline bool cdev_is_power_actor(struct thermal_cooling_device *cdev)
> >
> > int power_actor_get_max_power(struct thermal_cooling_device *,
> > struct thermal_zone_device *tz, u32 *max_power);
> > +int power_actor_get_min_power(struct thermal_cooling_device *,
> > + struct thermal_zone_device *tz, u32 *min_power);
> > int power_actor_set_power(struct thermal_cooling_device *,
> > struct thermal_instance *, u32);
> > struct thermal_zone_device *thermal_zone_device_register(const char *, int, int,
> > @@ -419,6 +421,10 @@ static inline bool cdev_is_power_actor(struct thermal_cooling_device *cdev)
> > static inline int power_actor_get_max_power(struct thermal_cooling_device *cdev,
> > struct thermal_zone_device *tz, u32 *max_power)
> > { return 0; }
> > +static inline int power_actor_get_min_power(struct thermal_cooling_device *cdev,
> > + struct thermal_zone_device *tz,
> > + u32 *min_power)
> > +{ return -ENODEV; }
>
> Perhaps return 0 like power_actor_get_max_power just above for
> consistency.

No, return 0 is not a good idea. If you return 0, you're telling the
calling function that everything went all right and you've put the
minimum power in @min_power.

What we should do is fix power_actor_get_max_power() and
power_actor_set_power() to return an error value if !CONFIG_THERMAL.

Cheers,
Javi