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MAN page from CentOS 7 kernel-plus-tools-3.10.0-1160.21.1.el7.centos.plus.x86_64.rpm

CPUPOWER-IDLE-INFO

Section: cpupower Manual (1)
Updated: 0.1
Index 

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. Thisinterface has been removed from the kernel for quite some time, do not letfurther 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 thesestatistics when it enters or leaves an idle state, therefore on a very idle ora very busy system, these statistics may not be accurate. They still provide agood overview about the usage and availability of processor sleep states onthe platform.

Be aware that the sleep states as exported by the hardware or BIOS and used bythe Linux kernel may not exactly reflect the capabilities of theprocessor. This often is the case on the X86 architecture when the acpi_idledriver is used. It is also possible that the hardware overrules the kernelrequests, due to internal activity monitors or other reasons.On recent X86 platforms it is often possible to read out hardware registerswhich monitor the duration of sleep states the processor resided in. Thecpupower monitor tool (cpupower-monitor(1)) can be used to show real sleepstate residencies. Please refer to the architecture specific descriptionsection 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 anypower. Instead, a busy-loop is executed doing nothing for a short period oftime. This state is used if the kernel knows that work has to be processedvery soon and entering any real hardware idle state may result in a slightperformance 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) fromthe ACPI BIOS tables (from the _CST ACPI function on recent platforms or fromthe 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 ornewer). On older Intel CPUs the acpi_idle driver is still used (if the BIOSprovides C-state ACPI tables).The intel_idle driver knows the sleep state capabilities of the processor andignores ACPI BIOS exported processor sleep states tables.

 

REMARKS

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

REFERENCES

http://www.acpi.info/spec.htm 

FILES

/sys/devices/system/cpu/cpu*/cpuidle/state*/sys/devices/system/cpu/cpuidle/*
 

AUTHORS

Thomas Renninger <trennAATTsuse.de>
 

SEE ALSO

cpupower(1), cpupower-monitor(1), cpupower-info(1), cpupower-set(1),cpupower-idle-set(1)


 

Index

NAME
SYNTAX
DESCRIPTION
OPTIONS
IDLE-INFO DESCRIPTIONS
IDLE-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS
X86
REMARKS
REFERENCES
FILES
AUTHORS
SEE ALSO

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