cpupower-idle-info - Online in the Cloud

PROGRAM:

NAME

cpupower idle-info - Utility to retrieve cpu idle kernel information

SYNTAX

cpupower [ -c cpulist ] idle-info [options]

DESCRIPTION

A tool which prints out per cpu idle information helpful to developers and interested
users.

OPTIONS

-f --silent
Only print a summary of all available C-states in the system.

-e --proc
deprecated. Prints out idle information in old /proc/acpi/processor/*/power
format. This interface has been removed from the kernel for quite some time, do not
let further code depend on this option, best do not use it.

IDLE-INFO DESCRIPTIONS

CPU sleep state statistics and descriptions are retrieved from sysfs files, exported by
the cpuidle kernel subsystem. The kernel only updates these statistics when it enters or
leaves an idle state, therefore on a very idle or a very busy system, these statistics may
not be accurate. They still provide a good overview about the usage and availability of
processor sleep states on the platform.

Be aware that the sleep states as exported by the hardware or BIOS and used by the Linux
kernel may not exactly reflect the capabilities of the processor. This often is the case
on the X86 architecture when the acpi_idle driver is used. It is also possible that the
hardware overrules the kernel requests, due to internal activity monitors or other
reasons. On recent X86 platforms it is often possible to read out hardware registers
which monitor the duration of sleep states the processor resided in. The cpupower monitor
tool (cpupower-monitor(1)) can be used to show real sleep state residencies. Please refer
to the architecture specific description section below.

IDLE-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS

X86
POLL idle state

If cpuidle is active, X86 platforms have one special idle state. The POLL idle state is
not a real idle state, it does not save any power. Instead, a busy-loop is executed doing
nothing for a short period of time. This state is used if the kernel knows that work has
to be processed very soon and entering any real hardware idle state may result in a slight
performance penalty.

There exist two different cpuidle drivers on the X86 architecture platform:

"acpi_idle" cpuidle driver

The acpi_idle cpuidle driver retrieves available sleep states (C-states) from the ACPI
BIOS tables (from the _CST ACPI function on recent platforms or from the FADT BIOS table
on older ones). The C1 state is not retrieved from ACPI tables. If the C1 state is
entered, the kernel will call the hlt instruction (or mwait on Intel).

"intel_idle" cpuidle driver

In kernel 2.6.36 the intel_idle driver was introduced. It only serves recent Intel CPUs
(Nehalem, Westmere, Sandybridge, Atoms or newer). On older Intel CPUs the acpi_idle driver
is still used (if the BIOS provides C-state ACPI tables). The intel_idle driver knows the
sleep state capabilities of the processor and ignores ACPI BIOS exported processor sleep
states tables.

REMARKS

By default only values of core zero are displayed. How to display settings of other cores
is described in the cpupower(1) manpage in the --cpu option section.

REFERENCES

http://www.acpi.info/spec.htm

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