Event-Based Thermal Control for High Power Density Microprocessors

This chapter presents the proposed event-based thermal control solution at the HARPA-RT level, thus complementing the previous chapter which dealt with the same topic at the HARPA-OS level. A brief analysis of the thermal control problem is presented, evidencing as the main requirement the need for thermal control at the millisecond timescale, caused by software variability in the use of CPU functional resources and fast thermal dynamics inside the silicon die. To meet this requirement while keeping a low overhead, the proposed solution consists of a hardware state machine and datapath that monitors temperature and generates interrupts, and a software policy built using event-based control theory. This partition provides both a fast response to critical and unpredictable temperature increases, a very low overhead when temperature is low or almost constant, and the flexibility of a software implementation of the control policy. The proposed solution is evaluated both in simulation using the Modelica modelling language, and on a commercial Intel CPU.