Closed-loop control for power and thermal management in multi-core processors: Formal methods and industrial practice

The need to use feedback to come up with context-dependent and workload-aware strategies for runtime power and thermal management (PTM) in high-end and mobile processors has been advocated since the early 2000. Two seminal papers that appeared in 2002 [1], [2] defined a framework for the use of feedback mechanisms for power and temperature control. In [1], the focus was on power management with the goal being to extend battery life on the AMD Mobile Athlon. This was one of the earliest papers to use DVFS settings as actuators to guarantee a given energy level in the battery at the end of a given time interval. The controller was implemented using a combination of OS files and Linux kernel modules. Almost simultaneously, [2] posed the dynamic thermal management task as a formal control-theoretic problem requiring the thermal modeling of the processor and the use of the established control structures of classical feedback theory. Some of the defining features of [2] include the development of layout-based thermal RC models for the processor; the use of an architecturally-driven control mechanism, namely, the instruction fetching rate; and the use of the SPEC2000 benchmarks to illustrate temperature control action under various workloads. The controller used in [2] is a Proportional-Integral-Differential (PID) structure whose input is the deviation of the sensed temperature from the target temperature and whose output is the toggle rate of the instruction fetching mechanism.