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authorAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-09-08 01:01:14 -0300
committerAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-09-08 01:01:14 -0300
commite5fd91f1ef340da553f7a79da9540c3db711c937 (patch)
treeb11842027dc6641da63f4bcc524f8678263304a3 /Documentation/thermal
parent2a9b0348e685a63d97486f6749622b61e9e3292f (diff)
Linux-libre 4.2-gnu
Diffstat (limited to 'Documentation/thermal')
-rw-r--r--Documentation/thermal/cpu-cooling-api.txt156
-rw-r--r--Documentation/thermal/power_allocator.txt247
-rw-r--r--Documentation/thermal/sysfs-api.txt99
3 files changed, 496 insertions, 6 deletions
diff --git a/Documentation/thermal/cpu-cooling-api.txt b/Documentation/thermal/cpu-cooling-api.txt
index 753e47cc2..71653584c 100644
--- a/Documentation/thermal/cpu-cooling-api.txt
+++ b/Documentation/thermal/cpu-cooling-api.txt
@@ -36,8 +36,162 @@ the user. The registration APIs returns the cooling device pointer.
np: pointer to the cooling device device tree node
clip_cpus: cpumask of cpus where the frequency constraints will happen.
-1.1.3 void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
+1.1.3 struct thermal_cooling_device *cpufreq_power_cooling_register(
+ const struct cpumask *clip_cpus, u32 capacitance,
+ get_static_t plat_static_func)
+
+Similar to cpufreq_cooling_register, this function registers a cpufreq
+cooling device. Using this function, the cooling device will
+implement the power extensions by using a simple cpu power model. The
+cpus must have registered their OPPs using the OPP library.
+
+The additional parameters are needed for the power model (See 2. Power
+models). "capacitance" is the dynamic power coefficient (See 2.1
+Dynamic power). "plat_static_func" is a function to calculate the
+static power consumed by these cpus (See 2.2 Static power).
+
+1.1.4 struct thermal_cooling_device *of_cpufreq_power_cooling_register(
+ struct device_node *np, const struct cpumask *clip_cpus, u32 capacitance,
+ get_static_t plat_static_func)
+
+Similar to cpufreq_power_cooling_register, this function register a
+cpufreq cooling device with power extensions using the device tree
+information supplied by the np parameter.
+
+1.1.5 void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
This interface function unregisters the "thermal-cpufreq-%x" cooling device.
cdev: Cooling device pointer which has to be unregistered.
+
+2. Power models
+
+The power API registration functions provide a simple power model for
+CPUs. The current power is calculated as dynamic + (optionally)
+static power. This power model requires that the operating-points of
+the CPUs are registered using the kernel's opp library and the
+`cpufreq_frequency_table` is assigned to the `struct device` of the
+cpu. If you are using CONFIG_CPUFREQ_DT then the
+`cpufreq_frequency_table` should already be assigned to the cpu
+device.
+
+The `plat_static_func` parameter of `cpufreq_power_cooling_register()`
+and `of_cpufreq_power_cooling_register()` is optional. If you don't
+provide it, only dynamic power will be considered.
+
+2.1 Dynamic power
+
+The dynamic power consumption of a processor depends on many factors.
+For a given processor implementation the primary factors are:
+
+- The time the processor spends running, consuming dynamic power, as
+ compared to the time in idle states where dynamic consumption is
+ negligible. Herein we refer to this as 'utilisation'.
+- The voltage and frequency levels as a result of DVFS. The DVFS
+ level is a dominant factor governing power consumption.
+- In running time the 'execution' behaviour (instruction types, memory
+ access patterns and so forth) causes, in most cases, a second order
+ variation. In pathological cases this variation can be significant,
+ but typically it is of a much lesser impact than the factors above.
+
+A high level dynamic power consumption model may then be represented as:
+
+Pdyn = f(run) * Voltage^2 * Frequency * Utilisation
+
+f(run) here represents the described execution behaviour and its
+result has a units of Watts/Hz/Volt^2 (this often expressed in
+mW/MHz/uVolt^2)
+
+The detailed behaviour for f(run) could be modelled on-line. However,
+in practice, such an on-line model has dependencies on a number of
+implementation specific processor support and characterisation
+factors. Therefore, in initial implementation that contribution is
+represented as a constant coefficient. This is a simplification
+consistent with the relative contribution to overall power variation.
+
+In this simplified representation our model becomes:
+
+Pdyn = Capacitance * Voltage^2 * Frequency * Utilisation
+
+Where `capacitance` is a constant that represents an indicative
+running time dynamic power coefficient in fundamental units of
+mW/MHz/uVolt^2. Typical values for mobile CPUs might lie in range
+from 100 to 500. For reference, the approximate values for the SoC in
+ARM's Juno Development Platform are 530 for the Cortex-A57 cluster and
+140 for the Cortex-A53 cluster.
+
+
+2.2 Static power
+
+Static leakage power consumption depends on a number of factors. For a
+given circuit implementation the primary factors are:
+
+- Time the circuit spends in each 'power state'
+- Temperature
+- Operating voltage
+- Process grade
+
+The time the circuit spends in each 'power state' for a given
+evaluation period at first order means OFF or ON. However,
+'retention' states can also be supported that reduce power during
+inactive periods without loss of context.
+
+Note: The visibility of state entries to the OS can vary, according to
+platform specifics, and this can then impact the accuracy of a model
+based on OS state information alone. It might be possible in some
+cases to extract more accurate information from system resources.
+
+The temperature, operating voltage and process 'grade' (slow to fast)
+of the circuit are all significant factors in static leakage power
+consumption. All of these have complex relationships to static power.
+
+Circuit implementation specific factors include the chosen silicon
+process as well as the type, number and size of transistors in both
+the logic gates and any RAM elements included.
+
+The static power consumption modelling must take into account the
+power managed regions that are implemented. Taking the example of an
+ARM processor cluster, the modelling would take into account whether
+each CPU can be powered OFF separately or if only a single power
+region is implemented for the complete cluster.
+
+In one view, there are others, a static power consumption model can
+then start from a set of reference values for each power managed
+region (e.g. CPU, Cluster/L2) in each state (e.g. ON, OFF) at an
+arbitrary process grade, voltage and temperature point. These values
+are then scaled for all of the following: the time in each state, the
+process grade, the current temperature and the operating voltage.
+However, since both implementation specific and complex relationships
+dominate the estimate, the appropriate interface to the model from the
+cpu cooling device is to provide a function callback that calculates
+the static power in this platform. When registering the cpu cooling
+device pass a function pointer that follows the `get_static_t`
+prototype:
+
+ int plat_get_static(cpumask_t *cpumask, int interval,
+ unsigned long voltage, u32 &power);
+
+`cpumask` is the cpumask of the cpus involved in the calculation.
+`voltage` is the voltage at which they are operating. The function
+should calculate the average static power for the last `interval`
+milliseconds. It returns 0 on success, -E* on error. If it
+succeeds, it should store the static power in `power`. Reading the
+temperature of the cpus described by `cpumask` is left for
+plat_get_static() to do as the platform knows best which thermal
+sensor is closest to the cpu.
+
+If `plat_static_func` is NULL, static power is considered to be
+negligible for this platform and only dynamic power is considered.
+
+The platform specific callback can then use any combination of tables
+and/or equations to permute the estimated value. Process grade
+information is not passed to the model since access to such data, from
+on-chip measurement capability or manufacture time data, is platform
+specific.
+
+Note: the significance of static power for CPUs in comparison to
+dynamic power is highly dependent on implementation. Given the
+potential complexity in implementation, the importance and accuracy of
+its inclusion when using cpu cooling devices should be assessed on a
+case by case basis.
+
diff --git a/Documentation/thermal/power_allocator.txt b/Documentation/thermal/power_allocator.txt
new file mode 100644
index 000000000..c3797b529
--- /dev/null
+++ b/Documentation/thermal/power_allocator.txt
@@ -0,0 +1,247 @@
+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. This is the first passive trip
+ point of the thermal zone.
+
+2. "desired temperature" trip point: it should be higher than the
+ "switch on" trip point. This the target temperature the governor
+ is controlling for. This is the last passive trip point of the
+ thermal zone.
+
+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_requested_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, the sustainable power of a 4" phone
+is typically 2000mW, while on a 10" tablet is around 4500mW (may vary
+depending on screen size).
+
+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>;
+ ...
+
+Instead, if the thermal zone is registered from the platform code, pass a
+`thermal_zone_params` that has a `sustainable_power`. If no
+`thermal_zone_params` were being passed, then something like below
+will suffice:
+
+ 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` configures the PID loop's derivative term constant. It's
+recommended to leave it as the default: 0.
+
+Cooling device power API
+========================
+
+Cooling devices controlled by this governor must supply the additional
+"power" API in their `cooling_device_ops`. It consists on three ops:
+
+1. int get_requested_power(struct thermal_cooling_device *cdev,
+ struct thermal_zone_device *tz, u32 *power);
+@cdev: The `struct thermal_cooling_device` pointer
+@tz: thermal zone in which we are currently operating
+@power: pointer in which to store the calculated power
+
+`get_requested_power()` calculates the power requested by the device
+in milliwatts and stores it in @power . It should return 0 on
+success, -E* on failure. This is currently used by the power
+allocator governor to calculate how much power to give to each cooling
+device.
+
+2. int state2power(struct thermal_cooling_device *cdev, struct
+ thermal_zone_device *tz, unsigned long state, u32 *power);
+@cdev: The `struct thermal_cooling_device` pointer
+@tz: thermal zone in which we are currently operating
+@state: A cooling device state
+@power: pointer in which to store the equivalent power
+
+Convert cooling device state @state into power consumption in
+milliwatts and store it in @power. It should return 0 on success, -E*
+on failure. This is currently used by thermal core to calculate the
+maximum power that an actor can consume.
+
+3. int power2state(struct thermal_cooling_device *cdev, u32 power,
+ unsigned long *state);
+@cdev: The `struct thermal_cooling_device` pointer
+@power: power in milliwatts
+@state: pointer in which to store the resulting state
+
+Calculate a cooling device state that would make the device consume at
+most @power mW and store it in @state. It should return 0 on success,
+-E* on failure. This is currently used by the thermal core to convert
+a given power set by the power allocator governor to a state that the
+cooling device can set. It is a function because this conversion may
+depend on external factors that may change so this function should the
+best conversion given "current circumstances".
+
+Cooling device weights
+----------------------
+
+Weights are a mechanism to bias the allocation among 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.
+
+If the thermal zone is registered using
+`thermal_zone_device_register()` (i.e., platform code), then weights
+are passed as part of the thermal zone's `thermal_bind_parameters`.
+If the platform is registered using device tree, then they are passed
+as the `contribution` property of each map in the `cooling-maps` node.
+
+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/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
index 87519cb37..c1f6864a8 100644
--- a/Documentation/thermal/sysfs-api.txt
+++ b/Documentation/thermal/sysfs-api.txt
@@ -95,7 +95,7 @@ temperature) and throttle appropriate devices.
1.3 interface for binding a thermal zone device with a thermal cooling device
1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
int trip, struct thermal_cooling_device *cdev,
- unsigned long upper, unsigned long lower);
+ unsigned long upper, unsigned long lower, unsigned int weight);
This interface function bind a thermal cooling device to the certain trip
point of a thermal zone device.
@@ -110,6 +110,8 @@ temperature) and throttle appropriate devices.
lower:the Minimum cooling state can be used for this trip point.
THERMAL_NO_LIMIT means no lower limit,
and the cooling device can be in cooling state 0.
+ weight: the influence of this cooling device in this thermal
+ zone. See 1.4.1 below for more information.
1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
int trip, struct thermal_cooling_device *cdev);
@@ -127,9 +129,15 @@ temperature) and throttle appropriate devices.
This structure defines the following parameters that are used to bind
a zone with a cooling device for a particular trip point.
.cdev: The cooling device pointer
- .weight: The 'influence' of a particular cooling device on this zone.
- This is on a percentage scale. The sum of all these weights
- (for a particular zone) cannot exceed 100.
+ .weight: The 'influence' of a particular cooling device on this
+ zone. This is relative to the rest of the cooling
+ devices. For example, if all cooling devices have a
+ weight of 1, then they all contribute the same. You can
+ use percentages if you want, but it's not mandatory. A
+ weight of 0 means that this cooling device doesn't
+ contribute to the cooling of this zone unless all cooling
+ devices have a weight of 0. If all weights are 0, then
+ they all contribute the same.
.trip_mask:This is a bit mask that gives the binding relation between
this thermal zone and cdev, for a particular trip point.
If nth bit is set, then the cdev and thermal zone are bound
@@ -176,6 +184,14 @@ Thermal zone device sys I/F, created once it's registered:
|---trip_point_[0-*]_type: Trip point type
|---trip_point_[0-*]_hyst: Hysteresis value for this trip point
|---emul_temp: Emulated temperature set node
+ |---sustainable_power: Sustainable dissipatable power
+ |---k_po: Proportional term during temperature overshoot
+ |---k_pu: Proportional term during temperature undershoot
+ |---k_i: PID's integral term in the power allocator gov
+ |---k_d: PID's derivative term in the power allocator
+ |---integral_cutoff: Offset above which errors are accumulated
+ |---slope: Slope constant applied as linear extrapolation
+ |---offset: Offset constant applied as linear extrapolation
Thermal cooling device sys I/F, created once it's registered:
/sys/class/thermal/cooling_device[0-*]:
@@ -192,6 +208,8 @@ thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
/sys/class/thermal/thermal_zone[0-*]:
|---cdev[0-*]: [0-*]th cooling device in current thermal zone
|---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
+ |---cdev[0-*]_weight: Influence of the cooling device in
+ this thermal zone
Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
the generic thermal driver also creates a hwmon sysfs I/F for each _type_
@@ -265,6 +283,14 @@ cdev[0-*]_trip_point
point.
RO, Optional
+cdev[0-*]_weight
+ The influence of cdev[0-*] in this thermal zone. This value
+ is relative to the rest of cooling devices in the thermal
+ zone. For example, if a cooling device has a weight double
+ than that of other, it's twice as effective in cooling the
+ thermal zone.
+ RW, Optional
+
passive
Attribute is only present for zones in which the passive cooling
policy is not supported by native thermal driver. Default is zero
@@ -289,6 +315,66 @@ emul_temp
because userland can easily disable the thermal policy by simply
flooding this sysfs node with low temperature values.
+sustainable_power
+ An estimate of the sustained power that can be dissipated by
+ the thermal zone. Used by the power allocator governor. For
+ more information see Documentation/thermal/power_allocator.txt
+ Unit: milliwatts
+ RW, Optional
+
+k_po
+ The proportional term of the power allocator governor's PID
+ controller during temperature overshoot. Temperature overshoot
+ is when the current temperature is above the "desired
+ temperature" trip point. For more information see
+ Documentation/thermal/power_allocator.txt
+ RW, Optional
+
+k_pu
+ The proportional term of the power allocator governor's PID
+ controller during temperature undershoot. Temperature undershoot
+ is when the current temperature is below the "desired
+ temperature" trip point. For more information see
+ Documentation/thermal/power_allocator.txt
+ RW, Optional
+
+k_i
+ The integral term of the power allocator governor's PID
+ controller. This term allows the PID controller to compensate
+ for long term drift. For more information see
+ Documentation/thermal/power_allocator.txt
+ RW, Optional
+
+k_d
+ The derivative term of the power allocator governor's PID
+ controller. For more information see
+ Documentation/thermal/power_allocator.txt
+ RW, Optional
+
+integral_cutoff
+ Temperature offset from the desired temperature trip point
+ above which the integral term of the power allocator
+ governor's PID controller starts accumulating errors. For
+ example, if integral_cutoff is 0, then the integral term only
+ accumulates error when temperature is above the desired
+ temperature trip point. For more information see
+ Documentation/thermal/power_allocator.txt
+ RW, Optional
+
+slope
+ The slope constant used in a linear extrapolation model
+ to determine a hotspot temperature based off the sensor's
+ raw readings. It is up to the device driver to determine
+ the usage of these values.
+ RW, Optional
+
+offset
+ The offset constant used in a linear extrapolation model
+ to determine a hotspot temperature based off the sensor's
+ raw readings. It is up to the device driver to determine
+ the usage of these values.
+ RW, Optional
+
*****************************
* Cooling device attributes *
*****************************
@@ -318,7 +404,8 @@ passive, active. If an ACPI thermal zone supports critical, passive,
active[0] and active[1] at the same time, it may register itself as a
thermal_zone_device (thermal_zone1) with 4 trip points in all.
It has one processor and one fan, which are both registered as
-thermal_cooling_device.
+thermal_cooling_device. Both are considered to have the same
+effectiveness in cooling the thermal zone.
If the processor is listed in _PSL method, and the fan is listed in _AL0
method, the sys I/F structure will be built like this:
@@ -340,8 +427,10 @@ method, the sys I/F structure will be built like this:
|---trip_point_3_type: active1
|---cdev0: --->/sys/class/thermal/cooling_device0
|---cdev0_trip_point: 1 /* cdev0 can be used for passive */
+ |---cdev0_weight: 1024
|---cdev1: --->/sys/class/thermal/cooling_device3
|---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
+ |---cdev1_weight: 1024
|cooling_device0:
|---type: Processor