Boreas: A Cost-Effective Mitigation Method for Advanced Hotspots using Machine Learning and Hardware Telemetry

Managing advanced hotspots on modern microprocessors is a critical and worsening issue, affecting performance, product reliability, and device lifetime. Many thermal management techniques focus primarily on remaining below a critical temperature, and while they are successful to that end, they come with a significant performance cost. This cost stems from the large temperature guardbands that are needed to ensure device safety and correct IC operation. These guardbands must be sized to account for multiple factors including 1) control-loop latency, 2) thermal sensor delay, 3) thermal gradients inside timing paths that could result in timing violations, and 4) the instantaneous temperature delta between a temperature sensor and the true peak temperature on the IC. This work demonstrates the need for novel hotspot avoidance techniques that can react quickly and simultaneously account for each of these concerns in order to safely maximize performance. Recently introduced hotspot metrics–Hotspot-Severity and Maximum Local Temperature Difference (MLTD)–are used in order to allow model designers to have a single optimization target that accounts for each of these thermal concerns simultaneously. We present Boreas, a novel hotspot mitigation technique that uses a Machine Learning model implemented in an on-chip specialized hardware accelerator that leverages micro-architectural performance counters. Boreas outperforms existing thermal management techniques while remaining lightweight and well-suited for implementation in hardware. Even with a conservative thermal sensor delay, Boreas is able to predict severity with high precision, resulting in effective hotspot mitigation on unseen workloads. These machine learning models were, therefore, able to select a frequency that was 4.5% better than thermal only models on average, and up to 9.6% higher in the best case, while having the same reliability budget as the thermal models.