The 195th R-CCS Cafe - part 3

The computing performance of the large-scale supercomputer is still growing even near the end of Moore's low. It is not easy to suppress the increase of the power consumption while growing up the performance. To reduce power consumption, many technologies have been developed and implemented ―for example, Hot-water cooling and Dynamic Voltage and Frequency Scaling (DVFS). The former is the technique to reduce cooling energy by using higher temperature cooling water, which can be cooled by outside air. The latter is a technique to cap CPU power consumption by automatic controlling the voltage and frequency depending on the load and the temperature of the CPU. The combination of the Hot-water cooling and DVFS is widely adopted to many large-scale systems and HPC centers. However, in the energy-saving aspect, it is non-trivial to show that this combination is effective. Because when Hot-water cooling and DVFS works, computing performance degradation will occur. In that case, we might need more energy to recover degradation. In this talk, I would like to introduce this issue in detail and our approach.