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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/pro-
              cessor/*/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, 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  pro-
       cessor  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  pro-
       cessed  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 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 pro-
       cessor 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 AT 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)