Reducing CPU Power Consumption for Low-Latency SSDs

Low-latency SSDs based on a new memory technology have been recently released in market. Their device latency is an order of magnitude lower than that of conventional NAND flash SSDs. With such a low latency, the operating frequency of a CPU core has a large impact on an I/O latency, because the time required for OS processing, which is executed on the core, accounts for a large proportion of it. In other words, an I/O latency is reduced as the core frequency is increased. However, a higher frequency causes a CPU to wastefully consume higher power during I/O wait times, because they are not long enough for the core to enter deep sleep states. In this work, we propose the device utilization-aware DVFS (DUDVFS) technique that periodically monitors the utilization of a storage device and decreases the voltages and frequencies of CPU cores only when it is fully utilized. As the storage device becomes a performance bottleneck in this case, DU-DVFS can reduce the CPU power consumption without hurting performance. Our evaluation with 28 I/O-intensive workloads on a real server containing an Intel® Optane" SSD demonstrates that DU-DVFS reduces the CPU power consumption by 43.7% on average (up to 56.3%) with a negligible performance degradation, compared to a standard Linux governor.