Characterization of smartphone governor strategies and making of a workload aware governor

This thesis presents the importance of workload characterization towards governing the operational voltage and frequency of a smartphone processor by running a series of workload on an ARM v8 processor. The idea of finishing a task as fast as possible to return to idle state(race-to-idle) versus the idea of choosing the correct frequency for time deltas(pace-to-idle) is studied in detail. Android governors either statically use a single frequency for the entire active time or determines the voltage and frequency dynamically based on the load average on the processor. Similar load averaging strategies are used for other blocks in SoC (System on Chip) like the GPU or the media processor. However, the different blocks of a SoC draw power from the same current source. Owing to lack of fine-grained workload characterization, the power is redirected to the not-so-important unit providing poor performance and energy efficiency. The behavior of different existing governors is explored by running on a variety of workload and analyze the optimal strategy for energy efficiency satisfying an acceptable user performance. Crucial traits of active user applications are inferred from scheduler to fine tune the optimal voltage and frequency across different blocks under constrained power source to build a system-wide governor.