Enabling Power-Aware Applications on Linux

Modern hardware devices that are idle for a certain period of time enter into sleep mode as a means of reducing power consumption. Naturally, devices should remain in sleep mode for as long as possible to maximize energy savings. However, a growing number of applications perform non-urgent background tasks, which may force hardware to wake up. It would be better if such non-urgent activities could be scheduled to execute only when the respective devices are already in use, as this would maximize the duration of sleep-states. This requires cooperation between applications and the kernel, as only the kernel can coordinate between applications that access the same hardware, and only applications know which tasks can be deferred and for how long. This paper presents the design and implementation of Cryogenic, a POSIX-compatible API that enables the clustering of tasks that access the same hardware. Specifically, the Cryogenic API allows applications to defer tasks until devices are used by other processes. This way, non-urgent tasks can choose not to wake up the device they require and instead defer their execution until either other tasks force the device to be powered on, or until the task becomes urgent. Cryogenic has been realized as a new Linux module, which integrates with the existing POSIX event loop system calls. This allows the use of Cryogenic on many different platforms, as long as the platform uses a Linux-kernel at the heart of the operating system. In addition to describing the design and implementation of Cryogenic, this paper contains experimental results that demonstrate Cryogenic’s ability to reduce power consumption using physical measurements on a Raspberry Pi.