New approaches to thermal management

Volker Eckert presented results from his experiments to use the CFS bandwidth controller for thermal management. The fundamental idea is to use less CPU bandwidth while running low-priority (background) tasks and thus keep the power budget available for more important tasks. This led to two interesting discussions: how to solve the per-entity load tracking (PELT) utilization issues for throttled tasks, and the idea, pushed by Morten Rasmussen, that thermal management should be applied to tasks rather than CPUs. Following this overall design approach, which was also backed by Paul Turner, the CFS bandwidth controller could play an essential role in a thermal-management architecture for future mobile systems.

Turner further suggested that the utilization should be scaled by using a non-throttled clock as a possible solution for the PELT problem. Another interesting point was raised as to whether the PELT utilization has to be propagated through the task-group hierarchy since there are no users of it for task groups. There is definitely some overlapping with the current "flatten CPU controller runqueues" patch set by Rik van Riel.

Eckert plans to continue his work by delivering a patch for this issue so it can be further discussed at the Linux Plumbers Conference later this year.