Proactive power management in IBM z15
The IBM z15 processor power management enhances several on-chip power management techniques over z14 processor with a specific focus on reducing response time for voltage droop management. The IBM z15 processor puts a specific emphasis on proactive voltage droop management strategy to reduce conservative static guard band that is added to the supply voltage in order to protect against worst-case voltage droops. The z15 processor relies on selected events from the earlier stages of a deep pipeline processor as indicators to predict sharp changes in the power consumption over a short period of time. The early information of the selected events allows to throttle the execution flow through the processor pipeline and prevents the sharp power change before it takes place and thus reduces the voltage droop. In z15, as one of the proactive schemes, we combine both the digital power-proxies, which are direct indicators of the processor activity and the Critical Path Monitors (CPMs) to give an earlier and proactive indication of voltage droop events. This proactive indication provides enough time for the throttle actuation circuits to prevent the voltage droop. CPMs act as real-time timing margin indicators, and power-proxies act to serve as the activity monitors.