Evaluation of DVFS and Uncore Frequency Tuning Under Power Capping on Intel Broadwell Architecture

In this paper we present an evaluation of the Intel Xeon Broadwell platform in the CINECA Galileo supercomputer when DVFS and UnCore Frequency (UCF) tuning is performed under the active power capping using RAPL powercap registers. This work is an extension of our previous work done under the H2020 READEX project which focused on a dynamic tuning of DVFS and UCF for complex HPC applications, but with no powercap limit enforced. Power capping is an essential technique that allows system administrators to maintain the power budget of an entire system or data center using either out-of-band management system or runtime systems such as GEOPM. In this paper we use two boundary workloads, Compute Bound Workload (CBW) and Memory Bound Workload (MBW) to show the behavior of the platform under power capping and potential for both energy and runtime savings when compared to the default CPU behavior. We show that DVFS and UCF tuning behave differently under the limited power budget. Our results show that if CPU has a limited power budget the proper tuning can provide both improved energy consumption as well as reduced runtime and that it is important to tune both DVFS and UCF. For MBW we can save up 22% for both runtime and energy when compared to default behavior under powercap. For CBW we can improve both performance, up to 9.4%, and energy consumption, up to 14.9%.