Messages in this thread | | | Subject | Re: [PATCH 2/4] Documentation/powercap/dtpm: Add documentation for dtpm | From | Ram Chandrasekar <> | Date | Tue, 13 Oct 2020 16:01:47 -0600 |
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On 10/6/2020 6:20 AM, Daniel Lezcano wrote: > The dynamic thermal and power management is a technique to dynamically > adjust the power consumption of different devices in order to ensure a > global thermal constraint. > > An userspace daemon is usually monitoring the temperature and the > power to take immediate action on the device. > > The DTPM framework provides an unified API to userspace to act on the > power. > > Document this framework. > > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> > --- > Documentation/power/powercap/dtpm.rst | 222 ++++++++++++++++++++++++++ > 1 file changed, 222 insertions(+) > create mode 100644 Documentation/power/powercap/dtpm.rst > > diff --git a/Documentation/power/powercap/dtpm.rst b/Documentation/power/powercap/dtpm.rst > new file mode 100644 > index 000000000000..ce11cf183994 > --- /dev/null > +++ b/Documentation/power/powercap/dtpm.rst > @@ -0,0 +1,222 @@ > +========================================== > +Dynamic Thermal Power Management framework > +========================================== > + > +On the embedded world, the complexity of the SoC leads to an > +increasing number of hotspots which need to be monitored and mitigated > +as a whole in order to prevent the temperature to go above the > +normative and legally stated 'skin temperature'. > + > +Another aspect is to sustain the performance for a given power budget, > +for example virtual reality where the user can feel dizziness if the > +performance is capped while a big CPU is processing something else. Or > +reduce the battery charging because the dissipated power is too high > +compared with the power consumed by other devices. > + > +The userspace is the most adequate place to dynamically act on the > +different devices by limiting their power given an application > +profile: it has the knowledge of the platform. > + > +The Dynamic Thermal Power Management (DTPM) is a technique acting on > +the device power by limiting and/or balancing a power budget among > +different devices. > + > +The DTPM framework provides an unified interface to act on the > +device power. > + > +=========== > +1. Overview > +=========== > + > +The DTPM framework relies on the powercap framework to create the > +powercap entries in the sysfs directory and implement the backend > +driver to do the connection with the power manageable device. > + > +The DTPM is a tree representation describing the power constraints > +shared between devices, not their physical positions. > + > +The nodes of the tree are a virtual description aggregating the power > +characteristics of the children nodes and their power limitations. > + > +The leaves of the tree are the real power manageable devices. > + > +For instance: > + > + SoC > + | > + `-- pkg > + | > + |-- pd0 (cpu0-3) > + | > + `-- pd1 (cpu4-5) > + > +* The pkg power will be the sum of pd0 and pd1 power numbers. > + > + SoC (400mW - 3100mW) > + | > + `-- pkg (400mW - 3100mW) > + | > + |-- pd0 (100mW - 700mW) > + | > + `-- pd1 (300mW - 2400mW) > + > +* When the nodes are inserted in the tree, their power characteristics > + are propagated to the parents. > + > + SoC (600mW - 5900mW) > + | > + |-- pkg (400mW - 3100mW) > + | | > + | |-- pd0 (100mW - 700mW) > + | | > + | `-- pd1 (300mW - 2400mW) > + | > + `-- pd2 (200mW - 2800mW) > + > +* Each node have a weight on a 2^10 basis reflecting the percentage of > + power consumption along the siblings. > + > + SoC (w=1024) > + | > + |-- pkg (w=538) > + | | > + | |-- pd0 (w=231) > + | | > + | `-- pd1 (w=794) > + | > + `-- pd2 (w=486) > + > + Note the sum of weights at the same level are equal to 1024. > + > +* When a power limitation is applied to a node, then it is distributed > + along the children given their weights. For example, if we set a > + power limitation of 3200mW at the 'SoC' root node, the resulting > + tree will be. > + > + SoC (w=1024) <--- power_limit = 3200mW > + | > + |-- pkg (w=538) --> power_limit = 1681mW > + | | > + | |-- pd0 (w=231) --> power_limit = 378mW > + | | > + | `-- pd1 (w=794) --> power_limit = 1303mW > + | > + `-- pd2 (w=486) --> power_limit = 1519mW > + > +==================== > +1.1 Flat description > +==================== > + > +A root node is created and it is the parent of all the nodes. This > +description is the simplest one and it is supposed to give to > +userspace a flat representation of all the devices supporting the > +power limitation without any power limitation distribution. > + > +============================ > +1.2 Hierarchical description > +============================ > + > +The different devices supporting the power limitation are represented > +hierarchically. There is one root node, all intermediate nodes are > +grouping the child nodes which can be intermediate nodes also or real > +devices. > + > +The intermediate nodes aggregate the power information and allows to > +set the power limit given the weight of the nodes. > + > +================ > +2. Userspace API > +================ > + > +As stated in the overview, the DTPM framework is built on top of the > +powercap framework. Thus the sysfs interface is the same, please refer > +to the powercap documentation for further details. > + > + * power_uw: Instantaneous power consumption. If the node is an > + intermediate node, then the power consumption will be the sum of all > + children power consumption. > + > + * max_power_range_uw: The power range resulting of the maximum power > + minus the minimum power. > + > + * name: The name of the node. This is implementation dependant. Even > + if it is not recommended for the userspace, several nodes can have > + the same name. > + > + * constraint_X_name: The name of the constraint. > + > + * constraint_X_max_power_uw: The maximum power limit to be applicable > + to the node. > + > + * constraint_X_power_limit_uw: The power limit to be applied to the > + node. If the value contained in constraint_X_max_power_uw is set, > + the constraint will be removed.
How is power_limit_uW different from max_power_uW?
> + > + * constraint_X_time_window_us: The meaning of this file will depend > + on the constraint number. > + > +=============== > +2.1 Constraints > +=============== > + > + * Constraint 0: The power limitation is immediately applied, without > + limitation in time. > + > +============= > +3. Kernel API > +============= > + > +============ > +3.1 Overview > +============ > + > +The DTPM framework has no power limiting backend support. It is > +generic and provides a set of API to let the different drivers to > +implement the backend part for the power limitation and create a the
create a the -> create a
> +power constraints tree. > + > +It is up to the platform to provide the initialization function to > +allocate and link the different nodes of the tree. > + > +A special macro has the role of declaring a node and the corresponding > +initialization function via a description structure. This one contains > +an optional parent field allowing to hook different devices to an > +already existing tree at boot time. > + > +struct dtpm_descr my_descr = { > + .name = "my_name", > + .init = my_init_func, > +}; > + > +DTPM_DECLARE(my_descr); > + > +The nodes of the DTPM tree are described with dtpm structure. The > +steps to add a new power limitable device is done in three steps: > + > + * Allocate the dtpm node > + * Set the power number of the dtpm node > + * Register the dtpm node > + > +The registration of the dtpm node is done with the powercap > +ops. Basically, it must implements the callbacks to get and set the
implements -> implement
> +power and the limit. > + > +Alternatively, if the node to be inserted is an intermediate one, then > +a simple function to insert it as a future parent is available. > + > +If a device has its power characteristics changing, then the tree must > +be updated with the new power numbers and weights. > + > +================ > +3.2 Nomenclature > +================ > + > + * dtpm_alloc() : Allocate and initialize a dtpm structure > + > + * dtpm_register() : Add the dtpm node to the tree > + > + * dtpm_register_parent() : Add an intermediate node > + > + * dtpm_unregister() : Remove the dtpm node from the tree > + > + * dtpm_update_power() : Update the power characteristics of the dtpm node >
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