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Servers running in datacenters are commonly kept underutilized to meet stringent latency targets. Due to poor energy-proportionality in commodity servers, the low utilization results in wasteful power consumption that cost millions of dollars. Applying dynamic power management on datacenter workloads is challenging, especially when tail latency requirements often fall in the sub-millisecond level. The fundamental issue is randomness due to unpredictable request arrival times and request service times. Prior techniques applied per-core DVFS to have fine-grain control of slowing down request processing without violating the tail latency target. However, most commodity servers only support per-core DFS, which greatly limits potential energy saving. In this paper, we propose DynSleep, a fine-grain power management scheme for datacenter workloads through the use of per-core sleep states (C-states). DynSleep …