Characterization of thermal coupling in chip multiprocessors
VanDerheyden, Andrew Louis
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For semiconductor processors temperature increases leakage current, which in turn in- creases the temperature of the processor. This increase in heat is seen by other parts of the processor since heat is diffusive across a processor die. In this way, cores are thermally coupled to one another such that when the temperature of one core increases, the temperatures of all cores on the same die can also increase. This increase in temperature and power consumption is not accompanied by any increase in performance. Cores on a chip can also be performance coupled to one another since cores can share data between them. These interactions between cores present new challenges to microarchitects who seek to optimize the energy consumption of a chip multiprocessor (CMP) comprised of multiple symmetric or asymmetric processing cores. This thesis seeks to understand and model the impact of thermal coupling effects between adjacent cores in a chip multiprocessor starting with measurements with a commercial multi-core processor. The hypothesis is that the thermal coupling of compute cores will be influenced by the adjacent core’s performance characteristics. Specifically, we expect thermal coupling is related to the nature of the workloads, e.g. compute intensive workloads will increase coupling over memory intensive workloads. However, we find that simpler parameters such as frequency of operation have more impact on coupling behaviors than the workload behaviors such as memory intensity or instruction retirement rates. A model is developed to capture thermal coupling effects and enable schemes to mitigate its impact.