CPUPOWER-IDLE-INFO(1) cpupower Manual CPUPOWER-IDLE-INFO(1)
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 re-
moved 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 up-
dates these statistics when it enters or leaves an idle state, there-
fore 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 avail-
ability 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 over-
rules 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 re-
sult in a slight performance penalty.
There exist two different cpuidle drivers on the X86 architecture plat-
form:
"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 pro-
vides 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 set-
tings of other cores is described in the cpupower(1) manpage in the
--cpu option section.
REFERENCES
https://uefi.org/specifications
FILES
/sys/devices/system/cpu/cpu*/cpuidle/state*
/sys/devices/system/cpu/cpuidle/*
AUTHORS
Thomas Renninger <trenn@suse.de>
SEE ALSO
cpupower(1), cpupower-monitor(1), cpupower-info(1), cpupower-set(1),
cpupower-idle-set(1)
0.1 CPUPOWER-IDLE-INFO(1)
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