Manual: cpupower-idle-info

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
	      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  availabil‐
       ity 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 re‐
       flect 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,  Sandy‐
       bridge,	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
       https://uefi.org/specifications

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

AUTHORS
       Thomas Renninger 

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

							     0.1				       CPUPOWER-IDLE-INFO(1)