How Power Capping Functions; Maintaining Power Consumption Below The Cap; Minimum And Maximum Power Consumption For A Server - Compaq BL10e - HP ProLiant - 512 MB RAM Introduction Manual

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 and uses P-states and/or clock throttling to limit processor power use to control overall
system power consumption. Whenever peak power consumption for a server exceeds the cap value
set by the administrator, the power capping control mechanism lowers the server's power
consumption below the cap in a controlled manner, regardless of changes in the server workload or
environment.
Server power consumption depends on many factors and can actually vary significantly over a given
period of time. Some factors, such as the number of options installed in the server, have a predictable
and static effect on server power consumption. Other factors -– including the temperature in the data
center, the activity of the subsystems (CPU, memory, disk drives and I/O) and even the mix of
instructions being executed – have a dynamic effect on power consumption. As long as the total
server power consumption does not exceed the power cap, there will be no effect on the server
workload.

Minimum and maximum power consumption for a server

To establish a set of guide posts to use when setting power caps, the power management system in
each server determines both the minimum and maximum power consumption for the server. These two
values are determined during the server's power-on self test (POST) by executing a set of tests that
measure the server power consumption in idle mode and under a simulated maximum load. Because
they are determined empirically, the minimum and maximum power values implicitly take into account
the server configuration and its current physical environment. The Insight Power Manager (IPM) and
iLO interfaces display both values, providing administrators with key information they can use to set
effective power caps.
The server power management system supplies one additional metric: maximum available power for
the server. For ProLiant ML and ProLiant DL servers this value is the maximum amount of power that
the server power supply is capable of producing. For HP BladeSystem servers, which are powered by
the enclosure's power supply array, the maximum available power represents the amount of power
reserved by the enclosure's Onboard Administrator for that particular server blade. This value is
reported in both iLO and Insight Power Manager. In iLO it is reported as ―Power supply maximum
power‖ for ML and DL servers and as ―Initial power-on request value‖ for BladeSystem servers.
Although they are initially determined during POST, minimum and maximum power consumption
values for a server can change slightly while the server is running. During normal operations, iLO and
the power management system continue to check both the five-minute average and the peak power
readings for the server. iLO will raise the maximum power consumption level if it measures a peak
value above the established maximum, and it will lower the minimum power consumption if it reads
an average power value that is below the present minimum.
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