Scalable System-level Active Low-Power Mode with Bounded Latency

Many system-level inactive low power modes exploit idle pe-riods to obtain energy savings. With the emergence of mul-ticore servers, idle periods are becoming increasingly rare. In order to save energy in multicore servers, low-utilization periods, which remains with increasing core count, must be exploited. Server-level heterogenous servers, such as Knight-Shift, have been shown to significantly improve the energy proportionality of datacenter servers through exploiting low-utilization periods. However, previous switching policies, which decides when to switch between a high-power high-performance node and a low-power lower-performance node, are simplistic and easily fooled by server utilization patterns, leading to false switches and thrashing causing unbounded latency impact. In this paper, we propose Hueristic-based Switching Policies (HSP), which uses utilization history to predict when fu-ture high utilization periods will occur. We show that HSP can significantly reduce thrashing and false switches, bound-ing latency while still maintaining significant energy savings. Furthermore, we show that active low-power modes that exploit low utilization periods are able to sustain energy-latency tradeoffs as core count increases and offer superior energy savings compared to idleness scheduling algorithms