Variability-Aware Voltage Island Management for Near-Threshold Computing with Performance Guarantees

The power-wall problem driven by the stagnation of supply voltages in deep-submicron technology nodes, is now the major scaling barrier for moving towards the manycore era. Although the technology scaling enables extreme volumes of computational power, power budget violations will permit only a limited portion to be actually exploited, leading to the so called dark silicon. Near-Threshold voltage Computing (NTC) has emerged as a promising approach to overcome the manycore power-wall, at the expenses of reduced performance values and higher sensitivity to process variations. Given that several application domains operate over specific performance constraints, the performance sustainability is considered a major issue for the wide adoption of NTC. Thus, in this chapter, we investigate how performance guarantees can be ensured when moving towards NTC manycores through variability-aware voltage and frequency allocation schemes. We propose three aggressive NTC voltage tuning and allocation strategies, showing that performance can be efficiently sustained or even optimized at the NTC regime. Finally, we show that NTC highly depends on the underlying workload characteristics, delivering average power gains of 65 % for thread-parallel workloads and up to 90 % for processparallel workloads, while offering an extensive analysis on the effects of different voltage tuning/ allocation strategies and voltage regulator configurations.