Software Engagement with Sleeping CPUs

Idle CPUs may enter power-saving hardware sleeps by, for instance, lowering the operating voltage and flushing the caches. However, wakeup delays that reach one hundred Secs or more are disrupting the operations of fast devices like solid-state disks and tightly integrated accelerators. On the other hand, maximal power savings on modern multicores are only realized through continuous, simultaneous CPU sleeps. We argue that strong software engagement (at the OS and applications) is needed to maximize the power saving while maintaining the desired performance. Specifically, we present anticipatory CPU wakeups for latency-sensitive operations on fast devices. We also explore power-saving sleep shaping opportunities through non-work-conserving scheduling on smartphones and staged bursts on servers.