System information
Power Management 143
11.3.2.2 Viewing and Modifying Kernel Idle
Statistics with cpupower
The idle-info subcommand shows the statistics of the cpuidle driver used in the
Kernel. It works on all architectures that use the cpuidle Kernel framework.
Example11.3: Example Output of cpupower idle-info
CPUidle driver: acpi_idle
CPUidle governor: menu
Analyzing CPU 0:
Number of idle states: 3
Available idle states: C1 C2
C1:
Flags/Description: ACPI FFH INTEL MWAIT 0x0
Latency: 1
Usage: 3156464
Duration: 233680359
C2:
Flags/Description: ACPI FFH INTEL MWAIT 0x10
Latency: 1
Usage: 273007117
Duration: 103148860538
After finding out which processor idle states are supported with cpupower idle-
info, individual states can be disabled using the cpupower idle-set com-
mand. Typically one wants to disable the deepest sleep state, for example:
cpupower idle-set -d 4
But before making this change permanent by adding the corresponding command to a
current /etc/init.d/* service file, check for performance or power impact.
11.3.2.3 Monitoring Kernel and Hardware
Statistics with cpupower
The most powerful enhancement is the monitor subcommand. Use it to report
processor topology, and monitor frequency and idle power state statistics over a cer-
tain period of time. The default interval is 1 second, but it can be changed with the -
i. Independent processor sleep states and frequency counters are implemented in the
tool—some retrieved from kernel statistics, others reading out hardware registers. The
available monitors depend on the underlying hardware and the system. List them with
cpupowermonitor-l. For a description of the individual monitors, refer to the
cpupower-monitor man page.