Memory access aware on-line voltage control for performance and energy optimization

This paper describes an off-chip memory access-aware runtime DVFS control technique that minimizes energy consumption subject to constraints on application execution times. We consider application phases and the implications of changing cache miss rates on the ideal power control state. We first propose a two-stage DVFS algorithm based on formulating the throughput-constrained energy minimization problem as a multiple-choice knapsack problem (MCKP). This algorithm uses a power model that adapts to application phase changes by observing processor hardware performance counter values. The solutions it produces provide upper bounds on the energy savings achievable under a performance constraint. However, this algorithm assumes a priori (oracle or profiling-based) knowledge of application phase change behavior. To relax this assumption, we propose P-DVFS, an predictive DVFS algorithm for on-line minimization of energy consumption under a performance constraint without requiring a priori knowledge of an application's behavior. P-DVFS uses hardware performance counter based performance and power models. It predicts remaining execution time online in order to control voltage and frequency settings to optimize energy consumption and performance. The P-DVFS problem is formulated as a multiple-choice knapsack problem, which can be efficiently and optimally solved online. We evaluated P-DVFS using direct measurement of a real DVFS-equipped system. When bounding performance loss to at most 20% of that at the maximum frequency and voltage, P-DVFS leads to energy consumptions within 1.83% of the optimal solution for our problem instances on average with a maximum deviation of 4.83%. In addition to producing results approaching those of an oracle formulation, P-DVFS reduces power consumption for our problem instances by 9.93% on average, and up to 25.64%, compared with the most advanced related work.