EVeREST-C: An Effective and Versatile Runtime Energy Saving Tool for CPUs

Power and energy efficiency are increasingly important challenges within HPC.However, it is still important to achieve these goals while maintaining desired/high application performance.Balancing these goals involves the challenge of precise application characterization.For successful user adoption, this must avoid modifying the application and/or extraneous application profiling, and also be portable to different processors across processor generations and vendors.We propose EVeREST-C to solve these challenges.Everest targets the finer-grained individual application functions for exploiting power/energy saving opportunities via Dynamic Voltage Frequency Scaling (DVFS) in both the core and the uncore, without application-specific knowledge.Since Everest relies on a single standard and accurate performance event, IPS (instructions per second), for its characterization rather than on the (many) performance counters that can differ across platforms, it is portable across processors.Finally, the fine-grained approach enables Everest to additionally save power/energy for select communication (MPI) phases, where appropriate phases are chosen based on both their length and position in the application with regards to the memory/compute boundedness of surrounding user routines.We evaluate Everest using SPEC CPU 2017 and various MPI applications, on Intel and AMD platforms.We find that Everest saves on average 11% more energy for SPEC compared to the baseline and 8% more energy on MPI applications compared to a state-of-the-art solution.