IBM Power 780 Technical Overview And Introduction page 130

Director Active Energy Manager (an IBM Systems Directors plug-in) for energy management
and control.
IBM EnergyScale makes use of power and thermal information collected from the system to
implement policies that can lead to better performance or better energy utilization. IBM
EnergyScale has the following features:
Power trending
EnergyScale provides continuous collection of real-time server energy consumption. It
enables administrators to predict power consumption across their infrastructure and to
react to business and processing needs. For example, administrators can use such
information to predict data center energy consumption at various times of the day, week,
or month.
Thermal reporting
IBM Director Active Energy Manager can display measured ambient temperature and
calculated exhaust heat index temperature. This information can help identify data center
hot spots that need attention.
Power saver mode
Power saver mode lowers the processor frequency and voltage on a fixed amount,
reducing the energy consumption of the system while still delivering predictable
performance. This percentage is predetermined to be within a safe operating limit and
is not user configurable. The server is designed for a fixed frequency drop of almost
30% down from nominal frequency (the actual value depends on the server type and
configuration). Power saver mode is not supported during boot or reboot, although it is
a persistent condition that will be sustained after the boot when the system starts
executing instructions.
Dynamic power saver mode
Dynamic power saver mode varies processor frequency and voltage based on the
utilization of the POWER7 or POWER7+ processors. Processor frequency and utilization
are inversely proportional for most workloads, implying that as the frequency of a
processor increases, its utilization decreases, given a constant workload. Dynamic power
saver mode takes advantage of this relationship to detect opportunities to save power,
based on measured real-time system utilization.
When a system is idle, the system firmware lowers the frequency and voltage to power
energy saver mode values. When fully utilized, the maximum frequency varies, depending
on whether the user favors power savings or system performance. If an administrator
prefers energy savings and a system is fully utilized, the system is designed to reduce the
maximum frequency to 95% of nominal values. If performance is favored over energy
consumption, the maximum frequency can be increased to up to 109% of nominal
frequency for extra performance.
Dynamic power saver mode is mutually exclusive with power saver mode. Only one of
these modes can be enabled at a given time.
Power capping
Power capping enforces a user-specified limit on power usage. Power capping is not a
power-saving mechanism. It enforces power caps by throttling the processors in the
system, degrading performance significantly. The idea of a power cap is to set a limit that
must never be reached but that frees up extra power never used in the data center. The
margined
installation in a data center. It is based on the server environmental specifications that
usually are never reached because server specifications are always based on maximum
116
IBM Power 770 and 780 (9117-MMD, 9179-MHD) Technical Overview and Introduction
power is this amount of extra power that is allocated to a server during its