Speaker
Description
The Linux thermal management and power capping frameworks currently evolve independently, despite relying on the same Energy Model (EM) to describe the power-performance characteristics of devices.
The thermal framework regulates temperature by estimating a sustainable power budget using the power_allocator governor. A PID control loop computes the power reduction required to maintain a target temperature, and the Energy Model translates this budget into Operating Performance Point (OPP) constraints applied through thermal cooling devices.
The powercap framework, and in particular the Dynamic Thermal Power Management (DTPM) controller, also relies on the Energy Model to enforce power budgets. However, instead of manipulating OPPs directly, it distributes power limits across a hierarchy of power domains.
Although both frameworks address closely related problems and use the same underlying model, there is currently no mechanism to connect them. This raises the question of whether a common abstraction could allow the thermal framework to express power constraints through the powercap hierarchy rather than through device-specific OPP constraints.
One possible direction is the introduction of a power cooling device, acting as a bridge between the thermal and powercap frameworks. Such an abstraction could enable thermal governors to allocate power budgets to powercap domains while leaving power distribution and enforcement to the powercap subsystem. This approach may also open the door to hierarchical power budgeting and more coordinated thermal management across heterogeneous devices.
The goal of this discussion is to explore whether this direction makes sense from an architectural perspective, identify the challenges involved, and agree on a set of incremental milestones that would allow such an integration to be developed and upstreamed progressively.