Re: [RFC PATCH v6 7/9] thermal: introduce the Power Allocator governor

Eduardo Valentin
2015-01-06T14:19:42Z

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On Tue, Jan 06, 2015 at 01:23:42PM +0000, Javi Merino wrote:
> Hi Eduardo,
>
> On Fri, Jan 02, 2015 at 03:46:24PM +0000, Eduardo Valentin wrote:
> > On Fri, Dec 05, 2014 at 07:04:18PM +0000, Javi Merino wrote:
> > > The power allocator governor is a thermal governor that controls system
> > > and device power allocation to control temperature. Conceptually, the
> > > implementation divides the sustainable power of a thermal zone among
> > > all the heat sources in that zone.
> > >
> > > This governor relies on "power actors", entities that represent heat
> > > sources. They can report current and maximum power consumption and
> > > can set a given maximum power consumption, usually via a cooling
> > > device.
> > >
> > > The governor uses a Proportional Integral Derivative (PID) controller
> > > driven by the temperature of the thermal zone. The output of the
> > > controller is a power budget that is then allocated to each power
> > > actor that can have bearing on the temperature we are trying to
> > > control. It decides how much power to give each cooling device based
> > > on the performance they are requesting. The PID controller ensures
> > > that the total power budget does not exceed the control temperature.
> > >
> > > Cc: Zhang Rui <rui.zhang@intel.com>
> > > Cc: Eduardo Valentin <edubezval@gmail.com>
> > > Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> > > Signed-off-by: Javi Merino <javi.merino@arm.com>
> > > ---
> > > Documentation/thermal/power_allocator.txt | 196 ++++++++++++
> > > drivers/thermal/Kconfig | 15 +
> > > drivers/thermal/Makefile | 1 +
> > > drivers/thermal/power_allocator.c | 511 ++++++++++++++++++++++++++++++
> > > drivers/thermal/thermal_core.c | 7 +-
> > > drivers/thermal/thermal_core.h | 8 +
> > > include/linux/thermal.h | 40 ++-
> > > 7 files changed, 774 insertions(+), 4 deletions(-)
> > > create mode 100644 drivers/thermal/power_allocator.c
> > >
> > > diff --git a/Documentation/thermal/power_allocator.txt b/Documentation/thermal/power_allocator.txt
> > > index d3bb79050c27..23b684afdc75 100644
> > > --- a/Documentation/thermal/power_allocator.txt
> > > +++ b/Documentation/thermal/power_allocator.txt
> > > @@ -1,3 +1,172 @@
> > > +Power allocator governor tunables
> > > +=================================
> > > +
> > > +Trip points
> > > +-----------
> > > +
> > > +The governor requires the following two passive trip points:
> > > +
> > > +1. "switch on" trip point: temperature above which the governor
> > > + control loop starts operating.
> > > +2. "desired temperature" trip point: it should be higher than the
> > > + "switch on" trip point. It is the target temperature the governor
> > > + is controlling for.
> > > +
> > > +PID Controller
> > > +--------------
> > > +
> > > +The power allocator governor implements a
> > > +Proportional-Integral-Derivative controller (PID controller) with
> > > +temperature as the control input and power as the controlled output:
> > > +
> > > + P_max = k_p * e + k_i * err_integral + k_d * diff_err + sustainable_power
> > > +
> > > +where
> > > + e = desired_temperature - current_temperature
> > > + err_integral is the sum of previous errors
> > > + diff_err = e - previous_error
> > > +
> > > +It is similar to the one depicted below:
> > > +
> > > + k_d
> > > + |
> > > +current_temp |
> > > + | v
> > > + | +----------+ +---+
> > > + | +----->| diff_err |-->| X |------+
> > > + | | +----------+ +---+ |
> > > + | | | tdp actor
> > > + | | k_i | | get_actual_power()
> > > + | | | | | | |
> > > + | | | | | | | ...
> > > + v | v v v v v
> > > + +---+ | +-------+ +---+ +---+ +---+ +----------+
> > > + | S |-------+----->| sum e |----->| X |--->| S |-->| S |-->|power |
> > > + +---+ | +-------+ +---+ +---+ +---+ |allocation|
> > > + ^ | ^ +----------+
> > > + | | | | |
> > > + | | +---+ | | |
> > > + | +------->| X |-------------------+ v v
> > > + | +---+ granted performance
> > > +desired_temperature ^
> > > + |
> > > + |
> > > + k_po/k_pu
> > > +
> > > +Sustainable power
> > > +-----------------
> > > +
> > > +An estimate of the sustainable dissipatable power (in mW) should be
> > > +provided while registering the thermal zone. This estimates the
> > > +sustained power that can be dissipated at the desired control
> > > +temperature. This is the maximum sustained power for allocation at
> > > +the desired maximum temperature. The actual sustained power can vary
> > > +for a number of reasons. The closed loop controller will take care of
> > > +variations such as environmental conditions, and some factors related
> > > +to the speed-grade of the silicon. `sustainable_power` is therefore
> > > +simply an estimate, and may be tuned to affect the aggressiveness of
> > > +the thermal ramp. For reference, this is 2000mW - 4500mW depending on
> > > +screen size (4" phone - 10" tablet).
> >
> > I would rephrase the example as:
> > 'For reference, the sustainable power of a 4" phone is typically 2000mW,
> > while on a 10" table is around 4500mW (may vary depending on screen
> > size).
>
> Ok
>
> > > +
> > > +If you are using device tree, do add it as a property of the
> > > +thermal-zone. For example:
> > > +
> > > + thermal-zones {
> > > + soc_thermal {
> > > + polling-delay = <1000>;
> > > + polling-delay-passive = <100>;
> > > + sustainable-power = <2500>;
> > > + ...
> > > +
> > > +If you use platform code to register your thermal zone instead, pass a
> > > +`thermal_zone_params` that has a `sustainable_power`. If you weren't
> > > +passing any `thermal_zone_params`, then something like this will do:
> > > +
> > > + static const struct thermal_zone_params tz_params = {
> > > + .sustainable_power = 3500,
> > > + };
> > > +
> > > +and then pass `tz_params` as the 5th parameter to
> > > +`thermal_zone_device_register()`
> > > +
> > > +k_po and k_pu
> > > +-------------
> > > +
> > > +The implementation of the PID controller in the power allocator
> > > +thermal governor allows the configuration of two proportional term
> > > +constants: `k_po` and `k_pu`. `k_po` is the proportional term
> > > +constant during temperature overshoot periods (current temperature is
> > > +above "desired temperature" trip point). Conversely, `k_pu` is the
> > > +proportional term constant during temperature undershoot periods
> > > +(current temperature below "desired temperature" trip point).
> > > +
> > > +These controls are intended as the primary mechanism for configuring
> > > +the permitted thermal "ramp" of the system. For instance, a lower
> > > +`k_pu` value will provide a slower ramp, at the cost of capping
> > > +available capacity at a low temperature. On the other hand, a high
> > > +value of `k_pu` will result in the governor granting very high power
> > > +whilst temperature is low, and may lead to temperature overshooting.
> > > +
> > > +The default value for `k_pu` is:
> > > +
> > > + 2 * sustainable_power / (desired_temperature - switch_on_temp)
> > > +
> > > +This means that at `switch_on_temp` the output of the controller's
> > > +proportional term will be 2 * `sustainable_power`. The default value
> > > +for `k_po` is:
> > > +
> > > + sustainable_power / (desired_temperature - switch_on_temp)
> > > +
> > > +Focusing on the proportional and feed forward values of the PID
> > > +controller equation we have:
> > > +
> > > + P_max = k_p * e + sustainable_power
> > > +
> > > +The proportional term is proportional to the difference between the
> > > +desired temperature and the current one. When the current temperature
> > > +is the desired one, then the proportional component is zero and
> > > +`P_max` = `sustainable_power`. That is, the system should operate in
> > > +thermal equilibrium under constant load. `sustainable_power` is only
> > > +an estimate, which is the reason for closed-loop control such as this.
> > > +
> > > +Expanding `k_pu` we get:
> > > + P_max = 2 * sustainable_power * (T_set - T) / (T_set - T_on) +
> > > + sustainable_power
> > > +
> > > +where
> > > + T_set is the desired temperature
> > > + T is the current temperature
> > > + T_on is the switch on temperature
> > > +
> > > +When the current temperature is the switch_on temperature, the above
> > > +formula becomes:
> > > +
> > > + P_max = 2 * sustainable_power * (T_set - T_on) / (T_set - T_on) +
> > > + sustainable_power = 2 * sustainable_power + sustainable_power =
> > > + 3 * sustainable_power
> > > +
> > > +Therefore, the proportional term alone linearly decreases power from
> > > +3 * `sustainable_power` to `sustainable_power` as the temperature
> > > +rises from the switch on temperature to the desired temperature.
> > > +
> > > +k_i and integral_cutoff
> > > +-----------------------
> > > +
> > > +`k_i` configures the PID loop's integral term constant. This term
> > > +allows the PID controller to compensate for long term drift and for
> > > +the quantized nature of the output control: cooling devices can't set
> > > +the exact power that the governor requests. When the temperature
> > > +error is below `integral_cutoff`, errors are accumulated in the
> > > +integral term. This term is then multiplied by `k_i` and the result
> > > +added to the output of the controller. Typically `k_i` is set low (1
> > > +or 2) and `integral_cutoff` is 0.
> > > +
> > > +k_d
> > > +---
> >
> > k_d may be conflicted with Kd (capacitance) of the cooling device power API.
> >
> > Is it possible to change / rename either one of them?
>
> You're right, I'll rename the one in the formula.
>
> > > +
> > > +`k_d` configures the PID loop's derivative term constant. It's
> > > +recommended to leave it as the default: 0.
> > > +
> > > Cooling device power API
> > > ========================
> > >
> > > @@ -25,3 +194,30 @@ milliwatts.
> > >
> > > Calculate a cooling device state that would make the device consume at
> > > most @power mW.
> > > +
> > > +Cooling device weights
> > > +----------------------
> > > +
> > > +Weights are a mechanism to bias the allocation between cooling
> > > +devices. They express the relative power efficiency of different
> > > +cooling devices. Higher weight can be used to express higher power
> > > +efficiency. Weighting is relative such that if each cooling device
> > > +has a weight of one they are considered equal. This is particularly
> > > +useful in heterogeneous systems where two cooling devices may perform
> > > +the same kind of compute, but with different efficiency. For example,
> > > +a system with two different types of processors.
> > > +
> > > +Weights shall be passed as part of the thermal zone's
> > > +`thermal_bind_parameters`.
> > > +
> > > +Limitations of the power allocator governor
> > > +===========================================
> > > +
> > > +The power allocator governor's PID controller works best if there is a
> > > +periodic tick. If you have a driver that calls
> > > +`thermal_zone_device_update()` (or anything that ends up calling the
> > > +governor's `throttle()` function) repetitively, the governor response
> > > +won't be very good. Note that this is not particular to this
> > > +governor, step-wise will also misbehave if you call its throttle()
> > > +faster than the normal thermal framework tick (due to interrupts for
> > > +example) as it will overreact.
> > > diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> > > index f554d25b4399..4496fa5e4a33 100644
> > > --- a/drivers/thermal/Kconfig
> > > +++ b/drivers/thermal/Kconfig
> > > @@ -71,6 +71,14 @@ config THERMAL_DEFAULT_GOV_USER_SPACE
> > > Select this if you want to let the user space manage the
> > > platform thermals.
> > >
> > > +config THERMAL_DEFAULT_GOV_POWER_ALLOCATOR
> > > + bool "power_allocator"
> > > + select THERMAL_GOV_POWER_ALLOCATOR
> > > + help
> > > + Select this if you want to control temperature based on
> > > + system and device power allocation. This governor relies on
> > > + power actors to operate.
> > > +
> > > endchoice
> > >
> > > config THERMAL_GOV_FAIR_SHARE
> > > @@ -99,6 +107,13 @@ config THERMAL_GOV_USER_SPACE
> > > help
> > > Enable this to let the user space manage the platform thermals.
> > >
> > > +config THERMAL_GOV_POWER_ALLOCATOR
> > > + bool "Power allocator thermal governor"
> > > + select THERMAL_POWER_ACTOR
> > > + help
> > > + Enable this to manage platform thermals by dynamically
> > > + allocating and limiting power to devices.
> >
> > I think the config entry deserves a better description, don't you
> > agree?
>
> Given that the entry for fair-share is "Enable this to manage platform
> thermals using fair-share governor." and the entry for step wise is
> "Enable this to manage platform thermals using a simple linear
> governor." this is actually pretty good ;)

hehehe... It does not mean we should follow bad examples right? :-)

>
> Instead of repeating in the config entry what is in the documentation,
> I think I'll put a pointer to
> Documentation/thermal/power_allocator.txt

Good!

>
> > > +
> > > config CPU_THERMAL
> > > bool "generic cpu cooling support"
> > > depends on CPU_FREQ
> > > diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> > > index 39c4fe87da2f..c33904848c45 100644
> > > --- a/drivers/thermal/Makefile
> > > +++ b/drivers/thermal/Makefile
> > > @@ -14,6 +14,7 @@ thermal_sys-$(CONFIG_THERMAL_GOV_FAIR_SHARE) += fair_share.o
> > > thermal_sys-$(CONFIG_THERMAL_GOV_BANG_BANG) += gov_bang_bang.o
> > > thermal_sys-$(CONFIG_THERMAL_GOV_STEP_WISE) += step_wise.o
> > > thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE) += user_space.o
> > > +thermal_sys-$(CONFIG_THERMAL_GOV_POWER_ALLOCATOR) += power_allocator.o
> > >
> > > # cpufreq cooling
> > > thermal_sys-$(CONFIG_CPU_THERMAL) += cpu_cooling.o
> > > diff --git a/drivers/thermal/power_allocator.c b/drivers/thermal/power_allocator.c
> > > new file mode 100644
> > > index 000000000000..09e98991efbb
> > > --- /dev/null
> > > +++ b/drivers/thermal/power_allocator.c
> > > @@ -0,0 +1,511 @@
> > > +/*
> > > + * A power allocator to manage temperature
> > > + *
> > > + * Copyright (C) 2014 ARM Ltd.
> > > + *
> > > + * This program is free software; you can redistribute it and/or modify
> > > + * it under the terms of the GNU General Public License version 2 as
> > > + * published by the Free Software Foundation.
> > > + *
> > > + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> > > + * kind, whether express or implied; without even the implied warranty
> > > + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> > > + * GNU General Public License for more details.
> > > + */
> > > +
> > > +#define pr_fmt(fmt) "Power allocator: " fmt
> > > +
> > > +#include <linux/rculist.h>
> > > +#include <linux/slab.h>
> > > +#include <linux/thermal.h>
> > > +
> > > +#include "thermal_core.h"
> > > +
> > > +#define FRAC_BITS 10
> > > +#define int_to_frac(x) ((x) << FRAC_BITS)
> > > +#define frac_to_int(x) ((x) >> FRAC_BITS)
> > > +
> > > +/**
> > > + * mul_frac() - multiply two fixed-point numbers
> > > + * @x: first multiplicand
> > > + * @y: second multiplicand
> > > + *
> >
> > If it is a kernel doc, needs a description.
>
> Other parts of the kernel are more liberal in this regard,
> specially fro trivial functions like this. Also, kernel-doc creates a
> documentation just fine:
>
> $ scripts/kernel-doc -function mul_frac drivers/thermal/power_allocator.c | nroff -man
> mul_frac(9) Kernel Hacker's Manual mul_frac(9)
>
>
>
> NAME
> mul_frac - multiply two fixed-point numbers
>
> SYNOPSIS
> s64 mul_frac (s64 x, s64 y);
>
> ARGUMENTS
> x first multiplicand
>
> y second multiplicand
>
> RETURN
> the result of multiplying two fixed-point numbers. The result is also
> a fixed-point number.
>
>
>
> January 2015 mul_frac mul_frac(9)
>
>
> I'll add the long description if you want to, but this is not a
> warning.
>

As long as there is no kerneldoc warning/errors, I am fine taking it. I
must confess I haven't run kerneldoc script in your patch as I got it
with encoding scrambled, so I was just pointing the missing entries.

> > > + * Return: the result of multiplying two fixed-point numbers. The
> > > + * result is also a fixed-point number.
> > > + */
> > > +static inline s64 mul_frac(s64 x, s64 y)
> > > +{
> > > + return (x * y) >> FRAC_BITS;
> > > +}
> > > +
> > > +enum power_allocator_trip_levels {
> > > + TRIP_SWITCH_ON = 0, /* Switch on PID controller */
> > > + TRIP_MAX_DESIRED_TEMPERATURE, /* Temperature we are controlling for */
> > > +
> > > + THERMAL_TRIP_NUM,
> > > +};
> > > +
> > > +/**
> > > + * struct power_allocator_params - parameters for the power allocator governor
> > > + * @k_po: Proportional parameter of the PID controller when overshooting
> > > + * (i.e., when temperature is below the target)
> > > + * @k_pu: Proportional parameter of the PID controller when undershooting
> > > + * @k_i: Integral parameter of the PID controller
> > > + * @k_d: Derivative parameter of the PID controller
> > > + * @integral_cutoff: threshold below which the error is no longer accumulated
> > > + in the PID controller
> > > + * @err_integral: accumulated error in the PID controller.
> > > + * @prev_err: error in the previous iteration of the PID controller.
> > > + * Used to calculate the derivative term.
> > > + */
> > > +struct power_allocator_params {
> > > + s32 k_po;
> > > + s32 k_pu;
> > > + s32 k_i;
> > > + s32 k_d;
> > > + s32 integral_cutoff;
> > > + s64 err_integral;
> > > + s32 prev_err;
> > > +};
> > > +
> > > +/**
> > > + * get_actor_weight() - get the weight for the power actor
> > > + * @tz: thermal zone we are operating in
> > > + * @actor: the power actor
> > > + *
> >
> >
> > ditto
> >
> > > + * Returns: The weight inside the thermal binding parameters of the
> >
> > s/Returns:/Return:/g
>
> Yep.
>
> > Please run the kernel doc script on your patches and avoid adding
> > warnings / errors.
>
> Actually, kernel-doc doesn't complain about Returns vs Return and it
> doesn't really care if there is no description in a function as I said
> before.
>
> Is there a better way than running "scripts/kernel-doc -function
> $FUNCTION $FILE" ? It would be great if scripts/check-patch.pl
> checked this as well.

I usually run
$ ./scripts/kernel-doc -text -v drivers/thermal/thermal_core.c > /dev/null

to see what it complain.

as for checkpatch.pl, well, I agree. But as it is not there, I have its
execution in my own internal scripts that I run on top of patches I
receive.

>
> > > + * thermal zone. If it could not be found, a default weight of 1 is
> > > + * assumed. Weights are expressed as a FRAC_BITS (currently 10-bit)
> > > + * fixed point integer.
> > > + */
> > > +static int get_actor_weight(struct thermal_zone_device *tz,
> > > + struct thermal_cooling_device *cdev)
> > > +{
> > > + int i;
> > > +
> > > + for (i = 0; i < tz->tzp->num_tbps; i++)
> > > + if (tz->tzp->tbp[i].cdev == cdev)
> > > + return tz->tzp->tbp[i].weight;
> > > +
> > > + return int_to_frac(1);
> > > +}
> > > +
> > > +/**
> > > + * pid_controller() - PID controller
> > > + * @tz: thermal zone we are operating in
> > > + * @current_temp: the current temperature in millicelsius
> > > + * @control_temp: the target temperature in millicelsius
> > > + * @max_allocatable_power: maximum allocatable power for this thermal zone
> > > + *
> > > + * This PID controller increases the available power budget so that the
> > > + * temperature of the thermal zone gets as close as possible to
> > > + * @control_temp and limits the power if it exceeds it. k_po is the
> > > + * proportional term when we are overshooting, k_pu is the
> > > + * proportional term when we are undershooting. integral_cutoff is a
> > > + * threshold below which we stop accumulating the error. The
> > > + * accumulated error is only valid if the requested power will make
> > > + * the system warmer. If the system is mostly idle, there's no point
> > > + * in accumulating positive error.
> > > + *
> > > + * Return: The power budget for the next period.
> > > + */
> > > +static u32 pid_controller(struct thermal_zone_device *tz,
> > > + unsigned long current_temp, unsigned long control_temp,
> > > + u32 max_allocatable_power)
> > > +{
> > > + s64 p, i, d, power_range;
> > > + s32 err, max_power_frac;
> > > + struct power_allocator_params *params = tz->governor_data;
> > > +
> > > + max_power_frac = int_to_frac(max_allocatable_power);
> > > +
> > > + err = ((s32)control_temp - (s32)current_temp);
> > > + err = int_to_frac(err);
> > > +
> > > + /* Calculate the proportional term */
> > > + p = mul_frac(err < 0 ? params->k_po : params->k_pu, err);
> > > +
> > > + /*
> > > + * Calculate the integral term
> > > + *
> > > + * if the error is less than cut off allow integration (but
> > > + * the integral is limited to max power)
> > > + */
> > > + i = mul_frac(params->k_i, params->err_integral);
> > > +
> > > + if (err < int_to_frac(params->integral_cutoff)) {
> > > + s64 i_next = i + mul_frac(params->k_i, err);
> > > +
> > > + if (abs64(i_next) < max_power_frac) {
> > > + i = i_next;
> > > + params->err_integral += err;
> > > + }
> > > + }
> > > +
> > > + /*
> > > + * Calculate the derivative term
> > > + *
> > > + * We do err - prev_err, so with a positive k_d, a decreasing
> > > + * error (i.e. driving closer to the line) results in less
> > > + * power being applied, slowing down the controller)
> > > + */
> > > + d = mul_frac(params->k_d, err - params->prev_err);
> > > + params->prev_err = err;
> > > +
> > > + power_range = p + i + d;
> > > +
> > > + /* feed-forward the known sustainable dissipatable power */
> > > + power_range = tz->tzp->sustainable_power + frac_to_int(power_range);
> > > +
> > > + return clamp(power_range, (s64)0, (s64)max_allocatable_power);
> > > +}
> > > +
> > > +/**
> > > + * divvy_up_power() - divvy the allocated power between the actors
> > > + * @req_power: each actor's requested power
> > > + * @max_power: each actor's maximum available power
> > > + * @num_actors: size of the @req_power, @max_power and @granted_power's array
> > > + * @total_req_power: sum of @req_power
> > > + * @power_range: total allocated power
> > > + * @granted_power: output array: each actor's granted power
> > > + *
> > > + * This function divides the total allocated power (@power_range)
> > > + * fairly between the actors. It first tries to give each actor a
> > > + * share of the @power_range according to how much power it requested
> > > + * compared to the rest of the actors. For example, if only one actor
> > > + * requests power, then it receives all the @power_range. If
> > > + * three actors each requests 1mW, each receives a third of the
> > > + * @power_range.
> > > + *
> > > + * If any actor received more than their maximum power, then that
> > > + * surplus is re-divvied among the actors based on how far they are
> > > + * from their respective maximums.
> > > + *
> > > + * Granted power for each actor is written to @granted_power, which
> > > + * should've been allocated by the calling function.
> > > + */
> > > +static void divvy_up_power(u32 *req_power, u32 *max_power, int num_actors,
> > > + u32 total_req_power, u32 power_range,
> > > + u32 *granted_power)
> > > +{
> > > + u32 extra_power, capped_extra_power, extra_actor_power[num_actors];
> > > + int i;
> > > +
> > > + if (!total_req_power) {
> > > + /*
> > > + * Nobody requested anything, so just give everybody
> > > + * the maximum power
> > > + */
> > > + for (i = 0; i < num_actors; i++)
> > > + granted_power[i] = max_power[i];
> > > +
> > > + return;
> > > + }
> > > +
> > > + capped_extra_power = 0;
> > > + extra_power = 0;
> > > + for (i = 0; i < num_actors; i++) {
> > > + u64 req_range = req_power[i] * power_range;
> > > +
> > > + granted_power[i] = div_u64(req_range, total_req_power);
> > > +
> > > + if (granted_power[i] > max_power[i]) {
> > > + extra_power += granted_power[i] - max_power[i];
> > > + granted_power[i] = max_power[i];
> >
> > shouldn't we continue here?
>
> No, you would leave the extra_actor_power[i] uninitialized.
>
> > > + }
> > > +
> > > + extra_actor_power[i] = max_power[i] - granted_power[i];
> >
> > Do we care when max_power[i] < granted_power[i]?
>
> That can't happen, the above "if" prevents it.
>
> > What happens to (overflowed) extra_actor_power[i]?
>
> extra_actor_power[i] can't overflow, it's a u32 and is asigned the
> result of substracting two u32s. The code make sure that the minuend is
> bigger or equal than the sustraend.
>

I see now. Maybe I need extra coffee :-)

> > > + capped_extra_power += extra_actor_power[i];
> > > + }
> > > +
> > > + if (!extra_power)
> > > + return;
> > > +
> > > + /*
> > > + * Re-divvy the reclaimed extra among actors based on
> > > + * how far they are from the max
> > > + */
> > > + extra_power = min(extra_power, capped_extra_power);
> > > + if (capped_extra_power > 0)
> > > + for (i = 0; i < num_actors; i++)
> > > + granted_power[i] += (extra_actor_power[i] *
> > > + extra_power) / capped_extra_power;
> > > +}
> > > +
> > > +static int allocate_power(struct thermal_zone_device *tz,
> > > + unsigned long current_temp, unsigned long control_temp)
> > > +{
> > > + struct thermal_instance *instance;
> > > + u32 *req_power, *max_power, *granted_power;
> > > + u32 total_req_power, max_allocatable_power;
> > > + u32 power_range;
> > > + int i, num_actors, ret = 0;
> > > +
> > > + mutex_lock(&tz->lock);
> > > +
> > > + num_actors = 0;
> > > + list_for_each_entry(instance, &tz->thermal_instances, tz_node)
> > > + if ((instance->trip == TRIP_MAX_DESIRED_TEMPERATURE) &&
> > > + cdev_is_power_actor(instance->cdev))
> > > + num_actors++;
> > > +
> > > + req_power = devm_kcalloc(&tz->device, num_actors, sizeof(*req_power),
> > > + GFP_KERNEL);
> > > + if (!req_power) {
> > > + ret = -ENOMEM;
> > > + goto unlock;
> > > + }
> > > +
> > > + max_power = devm_kcalloc(&tz->device, num_actors, sizeof(*max_power),
> > > + GFP_KERNEL);
> > > + if (!max_power) {
> > > + ret = -ENOMEM;
> > > + goto free_req_power;
> > > + }
> > > +
> > > + granted_power = devm_kcalloc(&tz->device, num_actors,
> > > + sizeof(*granted_power), GFP_KERNEL);
> > > + if (!granted_power) {
> > > + ret = -ENOMEM;
> > > + goto free_max_power;
> > > + }
> > > +
> > > + i = 0;
> > > + total_req_power = 0;
> > > + max_allocatable_power = 0;
> > > +
> > > + list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> > > + int weight;
> > > + struct thermal_cooling_device *cdev = instance->cdev;
> > > +
> > > + if (instance->trip != TRIP_MAX_DESIRED_TEMPERATURE)
> > > + continue;
> > > +
> > > + if (!cdev_is_power_actor(cdev))
> > > + continue;
> > > +
> > > + req_power[i] = cdev->ops->get_actual_power(cdev);
> >
> > Is this req_power (I read as 'requested power') or actual_power? I would
> > use the later naming to avoid confusions.
>
> We have had a lot of discussions internally about whether this should
> be the power that the device wants to consume or the power that is
> currently consuming. The current implementation in the cpu cooling
> device uses the power that the cpu is currently drawing because it's
> very hard to get the frequency that cpufreq would assign if there were
> no limits.
>
> I understand that it's confusing as it is, but I think it's better to
> rename get_actual_power() to get_requested_power() and explain this
> limitation in the kerneldoc for cpufreq_get_requested_power()
>

ok.

> > > + weight = get_actor_weight(tz, cdev);
> > > + req_power[i] = frac_to_int(weight * req_power[i]);
> > > + total_req_power += req_power[i];
> >
> > ditto for total_req_power.
> >
> > > +
> > > + max_power[i] = power_actor_get_max_power(cdev);
> > > + max_allocatable_power += max_power[i];
> > > +
> > > + i++;
> > > + }
> > > +
> > > + power_range = pid_controller(tz, current_temp, control_temp,
> > > + max_allocatable_power);
> > > +
> > > + divvy_up_power(req_power, max_power, num_actors, total_req_power,
> > > + power_range, granted_power);
> > > +
> > > + i = 0;
> > > + list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> > > + if (instance->trip != TRIP_MAX_DESIRED_TEMPERATURE)
> > > + continue;
> > > +
> > > + if (!cdev_is_power_actor(instance->cdev))
> > > + continue;
> > > +
> > > + power_actor_set_power(instance->cdev, granted_power[i]);
> > > +
> > > + i++;
> > > + }
> > > +
> > > + devm_kfree(&tz->device, granted_power);
> > > +free_max_power:
> > > + devm_kfree(&tz->device, max_power);
> > > +free_req_power:
> > > + devm_kfree(&tz->device, req_power);
> > > +unlock:
> > > + mutex_unlock(&tz->lock);
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static int check_trips(struct thermal_zone_device *tz)
> > > +{
> > > + int ret;
> > > + enum thermal_trip_type type;
> > > +
> > > + if (tz->trips < THERMAL_TRIP_NUM)
> > > + return -EINVAL;
> > > +
> > > + ret = tz->ops->get_trip_type(tz, TRIP_SWITCH_ON, &type);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + if (type != THERMAL_TRIP_PASSIVE)
> > > + return -EINVAL;
> > > +
> > > + ret = tz->ops->get_trip_type(tz, TRIP_MAX_DESIRED_TEMPERATURE, &type);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + if (type != THERMAL_TRIP_PASSIVE)
> > > + return -EINVAL;
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static void reset_pid_controller(struct power_allocator_params *params)
> > > +{
> > > + params->err_integral = 0;
> > > + params->prev_err = 0;
> > > +}
> > > +
> > > +static void allow_maximum_power(struct thermal_zone_device *tz)
> > > +{
> > > + struct thermal_instance *instance;
> > > +
> > > + list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> > > + u32 max_power;
> > > +
> > > + if ((instance->trip != TRIP_MAX_DESIRED_TEMPERATURE) ||
> > > + (!cdev_is_power_actor(instance->cdev)))
> > > + continue;
> > > +
> > > + max_power = power_actor_get_max_power(instance->cdev);
> > > + power_actor_set_power(instance->cdev, max_power);
> > > + }
> > > +}
> > > +
> > > +/**
> > > + * power_allocator_bind() - bind the power_allocator governor to a thermal zone
> > > + * @tz: thermal zone to bind it to
> > > + *
> > > + * Check that the thermal zone is valid for this governor, that is, it
> > > + * has two thermal trips. If so, initialize the PID controller
> > > + * parameters and bind it to the thermal zone.
> > > + *
> > > + * Return: 0 on success, -EINVAL if the trips were invalid or -ENOMEM
> > > + * if we ran out of memory.
> > > + */
> > > +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;
> > > +
> > > + ret = check_trips(tz);
> > > + if (ret) {
> > > + dev_err(&tz->device,
> > > + "thermal zone %s has the wrong number of trips for this governor\n",
> >
> > I would be more specific:
> > + "thermal zone %s has wrong trip setup for power allocator\n",
> >
> >
> > Besides, in 'check_trips' you check more than number of trips.
>
> Correct, I'll change the error message.
>
> > > + tz->type);
> > > + return ret;
> > > + }
> > > +
> > > + if (!tz->tzp || !tz->tzp->sustainable_power) {
> > > + dev_err(&tz->device,
> > > + "power_allocator: missing sustainable_power\n");
> > > + return -EINVAL;
> > > + }
> > > +
> > > + params = devm_kzalloc(&tz->device, sizeof(*params), GFP_KERNEL);
> > > + if (!params)
> > > + return -ENOMEM;
> > > +
> > > + ret = tz->ops->get_trip_temp(tz, TRIP_SWITCH_ON, &switch_on_temp);
> > > + if (ret)
> > > + goto free;
> > > +
> > > + ret = tz->ops->get_trip_temp(tz, TRIP_MAX_DESIRED_TEMPERATURE,
> > > + &control_temp);
> > > + if (ret)
> > > + goto free;
> > > +
> > > + temperature_threshold = control_temp - switch_on_temp;
> > > +
> > > + params->k_po = tz->tzp->k_po ?:
> > > + int_to_frac(tz->tzp->sustainable_power) / temperature_threshold;
> > > + params->k_pu = tz->tzp->k_pu ?:
> > > + int_to_frac(2 * tz->tzp->sustainable_power) /
> > > + temperature_threshold;
> > > + params->k_i = tz->tzp->k_i ?: int_to_frac(10) / 1000;
> > > + params->k_d = tz->tzp->k_d ?: int_to_frac(0);
> > > + params->integral_cutoff = tz->tzp->integral_cutoff ?: 0;
> > > +
> > > + reset_pid_controller(params);
> > > +
> > > + tz->governor_data = params;
> > > +
> > > + return 0;
> > > +
> > > +free:
> > > + devm_kfree(&tz->device, params);
> > > + return ret;
> > > +}
> > > +
> > > +static void power_allocator_unbind(struct thermal_zone_device *tz)
> > > +{
> > > + dev_dbg(&tz->device, "Unbinding from thermal zone %d\n", tz->id);
> > > + devm_kfree(&tz->device, tz->governor_data);
> > > + tz->governor_data = NULL;
> > > +}
> > > +
> > > +static int power_allocator_throttle(struct thermal_zone_device *tz, int trip)
> > > +{
> > > + int ret;
> > > + unsigned long switch_on_temp, control_temp, current_temp;
> > > + struct power_allocator_params *params = tz->governor_data;
> > > +
> > > + /*
> > > + * We get called for every trip point but we only need to do
> > > + * our calculations once
> > > + */
> > > + if (trip != TRIP_MAX_DESIRED_TEMPERATURE)
> > > + return 0;
> > > +
> > > + ret = thermal_zone_get_temp(tz, &current_temp);
> > > + if (ret) {
> > > + dev_warn(&tz->device, "Failed to get temperature: %d\n", ret);
> > > + return ret;
> > > + }
> > > +
> > > + ret = tz->ops->get_trip_temp(tz, TRIP_SWITCH_ON, &switch_on_temp);
> > > + if (ret) {
> > > + dev_warn(&tz->device,
> > > + "Failed to get switch on temperature: %d\n", ret);
> > > + return ret;
> > > + }
> > > +
> > > + if (current_temp < switch_on_temp) {
> > > + tz->passive = 0;
> > > + reset_pid_controller(params);
> > > + allow_maximum_power(tz);
> > > + return 0;
> > > + }
> > > +
> > > + tz->passive = 1;
> > > +
> > > + ret = tz->ops->get_trip_temp(tz, TRIP_MAX_DESIRED_TEMPERATURE,
> > > + &control_temp);
> > > + if (ret) {
> > > + dev_warn(&tz->device,
> > > + "Failed to get the maximum desired temperature: %d\n",
> > > + ret);
> > > + return ret;
> > > + }
> > > +
> > > + return allocate_power(tz, current_temp, control_temp);
> > > +}
> > > +
> > > +static struct thermal_governor thermal_gov_power_allocator = {
> > > + .name = "power_allocator",
> > > + .bind_to_tz = power_allocator_bind,
> > > + .unbind_from_tz = power_allocator_unbind,
> > > + .throttle = power_allocator_throttle,
> > > +};
> > > +
> > > +int thermal_gov_power_allocator_register(void)
> > > +{
> > > + return thermal_register_governor(&thermal_gov_power_allocator);
> > > +}
> > > +
> > > +void thermal_gov_power_allocator_unregister(void)
> > > +{
> > > + thermal_unregister_governor(&thermal_gov_power_allocator);
> > > +}
> > > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > > index c490f262ea7f..4921e084c20b 100644
> > > --- a/drivers/thermal/thermal_core.c
> > > +++ b/drivers/thermal/thermal_core.c
> > > @@ -1905,7 +1905,11 @@ static int __init thermal_register_governors(void)
> > > if (result)
> > > return result;
> > >
> > > - return thermal_gov_user_space_register();
> > > + result = thermal_gov_user_space_register();
> > > + if (result)
> > > + return result;
> > > +
> > > + return thermal_gov_power_allocator_register();
> > > }
> > >
> > > static void thermal_unregister_governors(void)
> > > @@ -1914,6 +1918,7 @@ static void thermal_unregister_governors(void)
> > > thermal_gov_fair_share_unregister();
> > > thermal_gov_bang_bang_unregister();
> > > thermal_gov_user_space_unregister();
> > > + thermal_gov_power_allocator_unregister();
> > > }
> > >
> > > static int __init thermal_init(void)
> > > diff --git a/drivers/thermal/thermal_core.h b/drivers/thermal/thermal_core.h
> > > index d15d243de27a..b907be823527 100644
> > > --- a/drivers/thermal/thermal_core.h
> > > +++ b/drivers/thermal/thermal_core.h
> > > @@ -85,6 +85,14 @@ static inline int thermal_gov_user_space_register(void) { return 0; }
> > > static inline void thermal_gov_user_space_unregister(void) {}
> > > #endif /* CONFIG_THERMAL_GOV_USER_SPACE */
> > >
> > > +#ifdef CONFIG_THERMAL_GOV_POWER_ALLOCATOR
> > > +int thermal_gov_power_allocator_register(void);
> > > +void thermal_gov_power_allocator_unregister(void);
> > > +#else
> > > +static inline int thermal_gov_power_allocator_register(void) { return 0; }
> > > +static inline void thermal_gov_power_allocator_unregister(void) {}
> > > +#endif /* CONFIG_THERMAL_GOV_POWER_ALLOCATOR */
> > > +
> > > /* device tree support */
> > > #ifdef CONFIG_THERMAL_OF
> > > int of_parse_thermal_zones(void);
> > > diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> > > index 1155457caf52..b23e019b1761 100644
> > > --- a/include/linux/thermal.h
> > > +++ b/include/linux/thermal.h
> > > @@ -61,6 +61,8 @@
> > > #define DEFAULT_THERMAL_GOVERNOR "fair_share"
> > > #elif defined(CONFIG_THERMAL_DEFAULT_GOV_USER_SPACE)
> > > #define DEFAULT_THERMAL_GOVERNOR "user_space"
> > > +#elif defined(CONFIG_THERMAL_DEFAULT_GOV_POWER_ALLOCATOR)
> > > +#define DEFAULT_THERMAL_GOVERNOR "power_allocator"
> > > #endif
> > >
> > > struct thermal_zone_device;
> > > @@ -255,9 +257,14 @@ struct thermal_bind_params {
> > >
> > > /*
> > > * This is a measure of 'how effectively these devices can
> > > - * cool 'this' thermal zone. The shall be determined by platform
> > > - * characterization. This is on a 'percentage' scale.
> > > - * See Documentation/thermal/sysfs-api.txt for more information.
> > > + * cool 'this' thermal zone. The shall be determined by
> > > + * platform characterization. For the fair-share governor,
> > > + * this is on a 'percentage' scale. See
> > > + * Documentation/thermal/sysfs-api.txt for more
> > > + * information. For the power_allocator governor, they are
> > > + * relative to each other, see
> > > + * Documentation/thermal/power_allocator.txt for more
> > > + * information.
> >
> > What happens if we register a thermal zone with relative weights, at
> > fist the user uses power allocator, but then wants to, for some reason,
> > use fair share? (or vice-versa).
> >
> > Can't power allocator use percentages too?
>
> The problem with percentages is that they are hard to use as they
> depend on each other. For example, you need to know how many cooling
> devices there are and that number needs to remain fixed. You can't
> add a new cooling device without changing the weights of all the other
> existing cooling devices. If the thermal zone is already created it's
> hard to change the weights so you really can't add or remove cooling
> devices.
>
> We were talking in another thread of ignoring a cooling device on some
> error. How do you do that if the percentages must add to a hundred?
>
> I thought that we could reuse the "weight" parameter but if you think
> we are abusing by making it mean different things for different
> governors we can create a new one instead.
>

yeah, I am concerned about the inconsistence. If you can make both
governor to use the data standardized with same unit (percentage or
relative values), then I am fine with that. Either way: (a) make power
allocator to use percentage; or (b) make fair share to use relative
values.

> Cheers,
> Javi
>

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