Specifications

Chapter 2. Architecture and technical overview 73
Draft Document for Review May 12, 2014 12:46 pm 5102ch02.fm
On POWER8 processor-based systems, several EnergyScale technologies are
embedded in the hardware and do not require an operating system or external
management component. Fan control, environmental monitoring and system energy
management are controlled by the On Chip Controller (OCC) and associated components.
The power mode can also be set up without external tools, by using the ASMI interface, as
shown in Figure 2-27.
Figure 2-27 Setting the power mode in ASMI
2.11.2 On Chip Controller
To maintain the power dissipation of POWER7+ in spite of its large increase in performance
and bandwidth, POWER8 invested significantly in power management innovations. A new
on-chip controller (OCC) utilizing an embedded PowerPC® core with 512 KB of SRAM runs
real-time control firmware to respond to workload variations by adjusting the per-core
frequency and voltage based on activity, thermal, voltage, and current sensors.
The on-die nature of the OCC allows for approximately 100× speed up in response to
workload changes over POWER7+, enabling reaction under the timescale of a typical OS
timeslice and allowing for multi-socket, scalable systems to be supported. It also enables
more granularity in controlling the energy parameters in the processor, and increases
reliability in energy management by having one controller in each processor that can perform
certain functions independently of the others.
POWER8 also includes an internal voltage regulation capability that enables each core to run
at a different voltage. Optimizing both voltage and frequency for workload variation enables
better increase in power savings versus optimizing frequency only.