System information
Power Management 135
Mode Definition
sor maintains all software-visible
states, but may take longer to wake up
through interrupts.
C3 Stops all CPU internal clocks. The
processor does not need to keep its
cache coherent, but maintains oth-
er states. Some processors have vari-
ations of the C3 state that differ in
how long it takes to wake the proces-
sor through interrupts.
To avoid needless power consumption, it is recommended to test your workloads with
deep sleep states enabled versus deep sleep states disabled. A recent maintenance
update for SUSE Linux Enterprise Server 11 SP3 provides an updated cpupow-
er package with an additional cpupower subcommand. Use it to disable or enable
individual C-states, if necessary. For more information, refer to Section11.3.2.2,
“Viewing and Modifying Kernel Idle Statistics with cpupower” (page143) or the
cpupower-idle-set(1) man page.
11.1.2 P-States (Processor Performance
States)
While a processor operates (in C0 state), it can be in one of several CPU performance
states (P-states). Whereas C-states are idle states (all but C0), P-states are
operational states that relate to CPU frequency and voltage.
The higher the P-state, the lower the frequency and voltage at which the processor
runs. The number of P-states is processor-specific and the implementation differs
across the various types. However, P0 is always the highest-performance state. Higher
P-state numbers represent slower processor speeds and lower power consumption. For
example, a processor in P3 state runs more slowly and uses less power than a proces-
sor running at P1 state. To operate at any P-state, the processor must be in the C0
state where the processor is working and not idling. The CPU P-states are also de-
fined in the Advanced Configuration and Power Interface (ACPI) specification, see
http://www.acpi.info/spec.htm.