CogniGron seminar-Computer Science dr. Shounak Chakraborty, NTNU, Norway

Managing thermal imbalance in contemporary chip multi-processors (CMPs) is crucial in assuring functional correctness of modern mobile as well as server systems. Localized regions with high activity, e.g., register files, ALUs, FPUs, etc., experience higher temperatures than the average across the chip and are commonly referred to as hotspots. Hotspots not only contribute to the increase cooling cost, but also affect functional correctness of the underlying circuitry and a noticeable increase in leakage power, which in turn generates heat in a self-reinforced cycle. Techniques that reduce the severity of or completely eliminate hotspots can maintain functional correctness along with improving performance of CMPs. Conventional dynamic thermal management targets the cores to reduce hotspots but often ignores caches, which are known for their high leakage power consumption. In this seminar, a recent technique, WaFFLe will be presented, that targets the leakage power of the last level cache (LLC) and hotspots occurring at the cores. WaFFLe turns off LLC-ways to reduce leakage power and to generate on-chip thermal buffers. In addition, fine-grained dynamic voltage and frequency scaling (DVFS) is applied during long LLC miss induced stalls to reduce core-temperature. Our results show, WaFFLe lowers peak and average temperature of a 16-core based homogeneous tiled CMP with up to 8.4°C and 6.2°C, respectively, while compromising performance by 2.5%, on average.