A Simple Model of Processor Temperature for Deterministic Turbo Clock Frequency
Résumé
As power dissipation and circuit temperature constrain their performance, modern processors feature turbo control mechanisms to adjust the voltage and clock frequency dynamically so that circuit temperature stays below a certain limit. In particular, turbo control exploits the fact that, after a long period of low processor activity, the thermal capacity of the chip, its package and the heatsink can absorb heat at a relatively fast rate during a certain time, before the temperature limit constrains that rate. Hence power dissipation can be temporarily boosted above the average sustainable value. The turbo control must monitor circuit temperature continuously to maximize the clock frequency. Temperature can be monitored by reading the integrated thermal sensors. However, making the clock frequency depend on thermal sensor readings implies that processor performance depends on ambient temperature. Yet this form of performance non-determinism is a problem for certain processor makers. A possible solution is to determine the clock frequency not from the true temperature but from a thermal model based on the nominal ambient temperature. Such model should be as accurate as possible in order to prevent sensor-based protection from triggering but sporadically, without hurting performance by overestimating temperature too much. The model should also be simple enough to provide calculated temperature in real time. This document proposes such thermal model and a turbo control based on that model.
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