TokenSmart: Distributed, Scalable Power Management in the Many-Core Era

Abstract

Centralized power management control systems are hitting a scalability limit. In particular, enforcing a power cap in a many-core system in a performance-friendly manner is quite challenging. Today’s on-chip controller reduces the clock speed of compute domains in response to local or global power limit alerts. However, this is transparent to the operating system (OS), which continues to request higher clock frequency based on the workload characteristics acting against the centralized on chip controller. To address these issues, we introduce TokenSmart, which implements a scalable distributed frequency control heuristics within the OS, using a novel token-based mechanism. The compute units are connected in a ring-topology allowing minimal meta-data to be passed along with the token value for regulating power budget. We explore different heuristics to assign tokens smartly across the units. This results in efficient power regulation and sustenance of turbo frequencies over a longer duration. The methodology is implemented within the Linux kernel of a real IBM POWER9 many-core system. The experimental results show a considerable boost of about 4 percent in throughput of PostgreSQL benchmark with a tangible 18 percent decrease in power consumption.