Combining Uncore Frequency and Dynamic Power Capping to Improve Power Savings

International audience; The US Department of Energy sets a limit of 20 to 30 MW for future exascale machines. In order to control their power consumption, modern processors provide many features. Power capping and uncore frequency scaling are examples of such features which allow to limit the power consumed by a processor. In this paper, we propose to combine dynamic power capping to uncore frequency scaling. We propose DUFP, an extension of DUF, an existing tool which dynamically adapts uncore frequency. DUFP dynamically adapts the processor power cap to the application needs. Finally, just like DUF, DUFP can tolerate performance loss up to a user-defined limit. With a controlled impact on performance, DUFP is able to provide power savings with no energy loss. The evaluation of DUFP shows that it manages to stay within the user-defined slowdown limits for most of the studied applications. Moreover, combining uncore frequency scaling to power capping: (i) improves power consumption by up to 13.98 % with additional energy savings for applications where uncore frequency scaling has a limited impact, (ii) improves power consumption by up to 7.90 % compared to using uncore frequency scaling by itself and (iii) leads to more than 5 % power savings at 5 % tolerated slowdown with no energy loss for most applications.