4
Figure 1. Power use in a typical server
Processor P-states
Processor performance states, or P-states, provide a quick and effective mechanism for adjusting processor power
consumption and performance. Both Intel
®
and AMD
®
processors support using P-states to decrease processor
power consumption by lowering the processor’s core frequency and voltage. Tables 1 and 2 list some of the P-states
available with different processors.
Table 1. P-states of the Intel Xeon 5160 processor
P-state Core Frequency
P0 3.0 GHz
P1 2.66 GHz
P2 2.33 GHz
P3 2.0 GHz
Table 2. P-states of the AMD Opteron 2220 processor
P- state Core Frequency
P0 2.8 GHz
P1 2.6 GHz
P2 2.4 GHz
P3 2.2 GHz
P4 2.0 GHz
P5 1.8 GHz
P6 1.0 GHz
Clock throttling
Clock throttling is another method for lowering processor power consumption. Depending on the processor model,
the system BIOS can either reprogram the processor to run at a lower frequency or modulate the processor between
running periods and stopped periods. Both methods have the same net effect of lowering the processor’s overall
power consumption below the levels available using P-states. The chart in Figure 2 illustrates the relationship
between consumed power and overall performance when using P-states and clock throttling to control server power.
Using P-states clearly provides greater power reduction for a smaller loss in performance. However, using P-states
can lower power consumption only to a certain point. Reducing consumption below that point requires the use of
clock throttling.
Typical Server Power Usage
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