DIMMer: A case of turning off DIMMs in clouds

Lack of energy proportionality in server systems results in significant waste of energy when operating at low utilization, a common scenario in today’s data centers. However, even during times of low utilization, servers cannot be powered off because of unpredictable spikes in instantaneous demand on some of the resources (e.g., file storage). To mitigate energy waste, unused processor cores transition into low-power sleep states, power-gating non-critical components; memory ranks (physical subdivisions of capacity) transition into selfrefresh modes, where energy is spent only to maintain memory contents. We propose DIMMer, an approach to entirely eliminate the idle power consumption of unused system components. DIMMer is motivated by two key observations. First, that even in their lowest-power states, the power consumption of today’s server components remains significant. Second, that unused components can be powered off entirely without sacrificing availability. We demonstrate that unused memory capacity can be turned off, eliminating the energy waste of self-refresh for unallocated memory, while still allowing for all capacity to be available on a moment’s notice. Similarly, only one CPU socket must remain powered on, allowing unused CPUs and attached memory to be powered off entirely. Leaving a single CPU powered on allows the server to remain fully operational and capable of rapidly ramping up to peak capacity if needed. In this work, we demonstrate the potential for DIMMer to improve energy proportionality and achieve energy savings. Using power measurements of a modern server system and data from a Google data center, we show up to 50% savings on DRAM and 18.8% on CPU background energy. Acknowledgement: This research was supported in part by NSF grants NSF CNS1161541, NSF CNS-1318572, NSF CNS-1223239, NSF CCF-0937833, by US ARMY award W911NF-13-1-0142, and by gifts from Northrop Grumman Corporation, Parc/Xerox, and Microsoft Research. Submission to SoCC ’14, October, 2014, Seattle, WA, USA.