At The Rack Level - Compaq BL10e - HP ProLiant - 512 MB RAM Introduction Manual

Figure 1. Data Center with Dynamic Power Capping
Actual aggregate Actual aggregate
power usage over time power usage over time

At the Rack Level

Dynamic Power Capping operates within each HP ProLiant server. In an HP BladeSystem
environment, it also functions at the enclosure level. Within individual rack-mount servers, the HP
Integrated Lights-Out (iLO 2) management processor works in conjunction with a power
microprocessor both to measure and control power usage. When enforcing the Dynamic Power
Cap, the power microcontroller first will lower the CPU p-state.
power has not been reached, the power microprocessor will continue to reduce CPU clock speed
to prevent peak power consumption from exceeding the user-defined cap. This process is
illustrated in Figure 2 below. Dynamic Power Caps for individual servers can be set from within
the iLO 2 Advanced user interface. Dynamic Power Caps for multiple rack-mount servers may be
set from the power management module within HP Insight Control Environment.
Since Dynamic Power Capping can impact server performance if set too aggressively, HP
recommends that Dynamic Power Caps be set at values that match or exceed the highest
observed power consumption over a representative server workload sample. Best practices for
setting Dynamic Power Caps will be discussed later in this paper.
3 A CPU p-state is a CPU frequency/voltage pair. By increase the P-state from P0 to P1 to P2, etc. both CPU frequency and voltage are
decreased. When computers operate at a lower p-state, they consume less power.
Allocated power capacity (per faceplate) Allocated power capacity (per faceplate)
Allocated power capacity (per power calculator) Allocated power capacity (per power calculator)
Hard cap of aggregate power Hard cap of aggregate power
with Dynamic Power Capping with Dynamic Power Capping
Time (hrs) Time (hrs)
3 If the required reduction in
4