Chapter 2. Architecture and technical overview
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The power mode can also be set up without external tools, by using the ASMI interface, as
shown in Figure 2-33.
Figure 2-33 Setting the power mode in ASMI
2.15.2 On Chip Controller
To maintain the power dissipation of with its large increase in performance and
bandwidth, POWER8 invested significantly in power management innovations. A new OCC
that uses an embedded IBM PowerPC® core with 512 KB of SRAM runs real-time control
firmware. It responds to workload variations by adjusting the per-core frequency and voltage
based on data from activity, thermal, voltage, and current sensors.
The on-die nature of the OCC allows for approximately 100× increase in speed in response to
workload changes over . The capability enables reaction under the time scale of a
typical OS time slice and allows 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.
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