How Power Capping Functions; Maintaining Power Consumption Below The Cap; Minimum And Maximum Power Consumption For A Server - HP Integrity NonStop NB54000c Introduction Manual

Figure 2. Power versus performance characteristics for a typical Intel-based ProLiant server with three P-states
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How power capping functions

Maintaining power consumption below the cap

With power capping, an administrator can set a maximum power consumption level for an individual server or for
a group of servers. The ProLiant power management system constantly monitors server power use. It adjusts P-states
and/or clock throttling to limit processor power use and control overall system power consumption. As needed, the
power capping control mechanism lowers the server's power consumption in a controlled manner to keep it below
the cap―without affecting the server workload or environment.
Server power consumption depends on many factors and can vary significantly over a given period. Some factors,
such as the number of options installed in the server, have a predictable and static effect on server power
consumption. Other factors have a dynamic effect on power consumption, for example the temperature in the data
center; the activity of the CPU, memory, disk drives, and I/O subsystems; and even the mix of instructions executed.
As long as the power consumption remains below the power cap, the power capping control mechanism takes no
action and there is no affect on server performance.

Minimum and maximum power consumption for a server

The power management system in each server determines both the minimum and maximum power consumption for
the server. It determines these two values during the server's power-on self test (POST) by executing tests measuring
server power consumption in idle mode and under a simulated maximum load. Because they are determined
empirically, the two power values implicitly take into account the server configuration and its current physical
environment. The Insight Control and iLO interfaces display both values to provide key information that
administrators can use to set effective power caps.
The power management system in the server supplies one additional metric: maximum available power for the
server. For ProLiant ML and ProLiant DL servers, this value is the maximum power that the server power supply can
DL360 G4 Power vs. Work Done
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